What each calendar is anchored to · where the year starts · the 24 solar terms · rabjung years · omitted and repeated days · three festival systems · background reading
29.53
days in a synodic month
365.2425
days in a Gregorian year
354
days in a common lunisolar year
1027
first year of the first rabjung
The short version
The Gregorian year is tied to the sun, the Islamic year to the moon, and the Chinese and Tibetan years to both — which is why the last two need leap months and the first two do not. Read the whole thing if you want the mechanics; read 01 and the table at the end if you only want to stop losing arguments about which day it is.
What is inside
- 01One day, three ways to count it
- 02Every calendar is anchored to one thing
- 03The year has begun on many different days
- 04Its frame is the 24 solar terms
- 05In 1582 ten days vanished
- 06It was assembled, not invented by one man
- 07Wood, fire, earth, metal, water — times twelve animals
- 08The fifteenth is always full moon
- 09A month apart, because the leaps differ
- 10Dates skip, and sometimes repeat
- 11A Tibetan year, and where its festivals fall
- 12Chinese festivals run on two frames
- 13Western festivals use three methods
- 14One table, three calendars side by side
- 15Fifteen Months, Three Calendars on One Axis
01 · INTRODUCTION
One day, three ways to count it
A day is a day. But the moment you pack it into years, months and dates, a grid has to be drawn — and different people drew the grid differently.
Three conventions still in use
Gregorian: sun only. A year is 365 days and a bit; the length of each month is a convention with no relation to the moon at all.
Hijri: moon only. Twelve synodic months make a year, about 354 days. Its festivals therefore drift about eleven days earlier each year.
Chinese and Tibetan: both. Months follow the moon, seasons follow the sun; when the two cycles refuse to line up, a leap month closes the gap.
Why the gap has to be closed
A synodic month is 29.53 days. Twelve of them make just over 354 — eleven days short of the 365.24-day tropical year.
Eleven days a year is a whole month every three years, and winter and summer swapped within a decade.
So any calendar that wants months to match the moon and seasons to match the sun must close that gap. The tool is the leap month.
It holds the other way too: whether a calendar needs leap months depends on whether it is trying to hold on to two things at once.
Do the arithmetic. 12 × 29.53 = 354.4 days. 365.24 − 354.4 = 10.9 days. Three years, one month short; nineteen years, seven. "Seven leap months in nineteen years" is not a decree — it is a division.
1
Meetings land on the wrong day. For the same ceremony, two calendars can give dates a day apart or a month apart. A day off is a wasted journey.
2
Last year's date will miss. Tibetan festivals move against the Gregorian calendar every year. A festival in February last year may fall in March this one.
3
Old records stall. Inscriptions and monastic histories often give a Tibetan year and no CE equivalent. Converting them means knowing the epoch and the rabjung.
The difference between the three is not accuracy. It is what each is willing to sacrifice: the Gregorian gives up the moon, the Hijri gives up the seasons, and the lunisolar pair refuses to give up either — at the price of a whole rulebook about leap months.
This booklet gives rules, not dates
Which date falls where changes every year. A printed booklet is fixed; the calendar is not — so what follows is the rules and the arithmetic, no specific dates. Locally, that year's almanac is the authority.
One common phrase to get out of the way. People often call the Chinese calendar "the lunar calendar". Strictly that is wrong: it contains the 24 solar terms, which are solar, and its leap months exist to keep up with the sun. The truly lunar calendar is the Hijri. The loose usage is old and there is no point correcting people — but it is worth knowing.
02 · I · THREE WAYS
Every calendar is anchored to one thing
Think of a calendar as a rope with one end in the sky and one on the ground. Whether it is tied to the sun or to the moon decides its character — and what it has to pay.
Gregorian
To the sun
A year = the tropical year, 365.2422 days. Month lengths are pure legacy: August's 31st day was borrowed from February. Cost: the moon is ignored, so "the moon on the fifteenth" means nothing here.
Lunar
To the moon
A year = twelve synodic months ≈ 354.36 days. Months always match the phases; a new moon is always day one. Cost: the year runs eleven days short, so Ramadan drifts from winter into summer, a full circuit in about 33 years.
Lunisolar
To both
Months to the phases, seasons to the sun. Cost: leap months become unavoidable, and deciding which month to double is the hardest arithmetic in the whole business.
Three cycles, no common multiple
The Earth's rotation gives the day; the Moon's orbit, 29.53 days; the Earth's orbit, 365.2422 days. None is a whole multiple of another.
Leap months, leap days, omitted days, repeated days — every one of them is a patch on that mismatch.
Leap months, leap days, omitted days, repeated days — every one of them is a patch on that mismatch.
| Gregorian | Lunar | Chinese · Tibetan | |
|---|---|---|---|
| A month | 28–31 days, by convention | 29 or 30, following the moon | 29 or 30, following the moon |
| A year | 365 or 366 days | about 354 days | about 354; 383–385 in a leap year |
| New year | always in winter | eleven days earlier each year | late winter to early spring |
One line to keep: the Gregorian follows the sun, the lunar follows the moon, and the Chinese and Tibetan calendars try to follow both — which is exactly why they are the complicated ones.
"Solar" does not mean Gregorian
The Julian, Iranian and Ethiopian calendars are all solar; the Gregorian is simply the most widely used. Likewise "lunar" does not mean Hijri only — early Greek and Roman months ran on the moon. The categories describe what a calendar is anchored to, not who came first.
"Accurate" is not the same as "usable". The Gregorian is the most accurate but blind to the moon; the lunar is perfect on phases but lets the seasons slide; the Chinese and Tibetan pair does both jobs imperfectly and fits an agricultural life best. Judge a calendar by the problem it was built to solve.
03 · I · THE START OF THE YEAR
The year has begun on many different days
"New year" means "the first morning". Which morning counts as the first, different calendars have answered very differently — and where you put it decides which season your festivals land in.
The winter
solstice
solstice
The year once began at the solstice. The logic is plain: this is the longest shadow, and from the next day the light grows. Pre-Han practice put the start of the year there; later calendars kept the solstice as an internal reference point and stopped calling it New Year.
The start
of spring
of spring
The first of the 24 solar terms. In some years the Spring Festival falls right beside it and the two get treated as one thing — but the festival is fixed by the first day of the first lunar month, and the start of spring by the sun. Two systems.
1st day,
1st lunar month
1st lunar month
Fixed at the new moon of the month containing the "rain water" term. That is why the Spring Festival always falls between late January and mid-February: lunar by definition, boxed in by a solar term.
The grain
harvest
harvest
Tibet's year once began when the grain ripened. The New Tang History records of the Tibetans: "In their four seasons, they take the ripening of grain as the start of the year." Not astronomy — watching the crop. The trace of a phenological calendar.
1 March
old Rome
old Rome
The Roman year began in March. Hence September, literally "seventh", October "eighth", November "ninth", December "tenth" — names left over from a year that started in March.
1 January
Gregorian
Gregorian
Rome later moved the start to 1 January and the Gregorian kept it. The "1 January" printed on every calendar today is that decision winning.
Behind the start of the year lie three unrelated threads: astronomy (the solstice), phenology (the harvest), administration (Rome moving the year from March to January). The answer in use today is the third.
The Spring Festival and the start of spring
These are a fortnight apart as a rule. One is fixed by the new moon, the other by the sun. They coincide in some years; in most they are half a month apart. Calling the Spring Festival "the start of spring" merges two systems into one.
Move the start of the year and the bookkeeping breaks. After Rome moved the year to January, month names and month numbers stopped agreeing — December, literally "tenth", is now the twelfth month. The name stayed where it was; the number moved on.
04 · I · THE CHINESE CALENDAR
Its frame is the 24 solar terms
The Chinese calendar is usually called lunar, but what has kept it from drifting out of season for two thousand years is not the moon. It is a solar scale hidden inside it.
1
Months carry the phases, solar terms carry the seasons. The first of a month is the new moon, the fifteenth the full; the terms divide the sun's path into 15-degree steps. Set side by side, the calendar reads the moon and still cannot put June in winter.
2
The leap month closes the gap. Twelve lunar months make about 354 days, eleven short of a tropical year. The old rule was seven leap months in nineteen years. The current rule is sharper: the month that contains no mid-term becomes the leap month.
3
A leap month takes the number of the one before it. A leap fourth month is a second fourth month. So a Chinese year can hold thirteen months and run 383 to 385 days.
4
Long and short months are not fixed. A month is 29 or 30 days, decided by when the new moon falls — nothing to memorise. "Thirty days a month" is simply wrong.
The solar-term rhyme — a mnemonic still taught in schools, four lines of seven characters:
Spring rain, awakening, clear and bright, grain rain; summer begins, grain full, grain in ear, solstice, minor heat, major heat; autumn begins, heat ends, white dew, equinox, cold dew, frost descends; winter begins, light snow, heavy snow, solstice, minor cold, great cold.
What a "mid-term" is
The 24 terms fall into two sets. The twelve at odd positions are the nodal terms; the twelve at even positions are the mid-terms (rain water, spring equinox, grain rain, grain full, summer solstice, major heat, end of heat, autumn equinox, frost descent, light snow, winter solstice, major cold).
A synodic month is 29.53 days and two mid-terms are about 30.44 days apart. The month is shorter, so every two or three years one month misses a mid-term. That month becomes the leap month.
A synodic month is 29.53 days and two mid-terms are about 30.44 days apart. The month is shorter, so every two or three years one month misses a mid-term. That month becomes the leap month.
Clear and Bright is the only solar term that turned into a festival. Every other major one — New Year, Dragon Boat, Mid-Autumn, Double Ninth — is fixed by the moon. Only this is fixed by the sun. Which is why it barely moves, while the Spring Festival can shift by a month.
The 24 solar terms are not universal. They were defined for the climate of the middle and lower Yellow River. Change latitude or altitude and the phenology stops matching — spring arrives far later on the plateau than the terms suggest. Which is why the Tibetan calendar keeps a different division of the year; see page 06.
05 · I · THE GREGORIAN
In 1582 ten days vanished
The Gregorian calendar was not calculated right once and for all. It was repaired. In the year of the repair, the day after 4 October was 15 October — the ten days between never happened.
1
The Julian drift. Caesar's calendar averaged 365.25 days, eleven minutes fourteen seconds longer than the tropical year. Invisible in a year; a whole day every 128 years.
2
The drift broke Easter. The Council of Nicaea in 325 ruled that Easter falls on the first Sunday after the first full moon following the spring equinox, with the equinox fixed at 21 March. By the sixteenth century the real equinox had slipped to 11 March and the feast could no longer be computed.
3
The repair. In 1582 Gregory XIII issued a new calendar: drop ten days to pull the equinox back to 21 March, and change the leap rule to "every four years, except every hundred, except every four hundred" — 97 leap years in 400.
| Year | Leap? | Why |
|---|---|---|
| 1600 | yes | divisible by 400 |
| 1700 | no | divisible by 100, not by 400 |
| 1900 | no | same |
| 2000 | yes | divisible by 400 |
| 2100 | no | same |
Others changed later, so the ledger is messier
England waited until 1752 and had to drop eleven days (2 September was followed by 14 September); Russia waited until 1918 and dropped thirteen. Which is why the October Revolution happened in October by the Russian calendar and on 7 November by the Gregorian. One event, two dates — not a mistake, just no calendar change.
The Gregorian year averages 365.2425 days, three ten-thousandths off the tropical 365.2422. It takes over three thousand years to lose a day — accurate enough for a calendar meant for everyone.
06 · II · THE TIBETAN CALENDAR
It was assembled, not invented by one man
Not an algorithm built from nothing, but three layers stacked: local phenology at the base, Kalachakra from India, the Shixian calendar from China. Take any layer away and it is no longer this calendar.
Phenological
local
local
The oldest layer. Planting times read off plants, birds and beasts, with no heavy computation. The early practice of taking the ripening of grain as the start of the year is its trace. The six-season division survives today: spring, late spring, summer, autumn, winter, late winter.
Kalachakra
India
India
Arrived in the eleventh century. The Kalachakra Tantra brought a complete astronomy: how to compute eclipses, how the five planets move, how to cut the year into months and days. This layer became the backbone.
Shixian
China
China
Introduced in the Qing. After several centuries the Kalachakra calculations had drifted, and under the Fifth Dalai Lama and the Kangxi emperor the more precise Shixian calendar was absorbed as a correction.
The calendar
today
today
Kalachakra as the frame, with parts of the Shixian method absorbed. The almanac compiled by Tibet's astronomical institute today runs on exactly this.
Phenology left
The crop
Ongkor is not fixed to a month and day but to whether the barley is ripe. The oldest layer, still running.
Kalachakra left
Omitted days
Dates that skip and dates that repeat — not a habit, a direct result of the Kalachakra arithmetic.
Shixian left
Solar terms
Tibetan almanacs also carry the 24 solar terms as reference points, used to correct the drift.
Both short versions are wrong. "It was imported from India" is wrong — it holds local phenology and the Chinese Shixian method. "It was copied from the Chinese calendar" is wrong too — the backbone is Kalachakra. Calling it a fusion is not politeness; it is the fact.
Why the epoch is 1027
The preceding year was reckoned a "year of exhaustion": sun, moon, the five planets and the nine luminaries all in the same quarter, everything returning to zero. Counting restarted the year after. In the Tibetan reckoning it was the female Fire Rabbit, in the Chinese the ding-mao year. From there, sixty-year cycles run, called rabjung.
Of the three, the Tibetan is the only one that can name the year its count began. The Gregorian epoch was assigned after the fact; the Chinese sexagenary cycle has no absolute start; only here is year one nailed to a date.
07 · II · YEARS
Wood, fire, earth, metal, water — times twelve animals
The Tibetan calendar uses neither CE years nor the Chinese stem-and-branch names. It stacks five elements onto twelve animals and turns a cycle every sixty years — the same logic as the Chinese sexagenary cycle, with two words swapped.
| Tibetan | Chinese | Note |
|---|---|---|
| female Fire Rabbit | ding-mao | 1027, first year of the first rabjung |
| male Fire Horse | bing-wu | 1966 and 2026, sixty years apart |
| female Earth Ox | ji-chou | 2009 |
| female Metal Snake | xin-si | 2001 |
1
The mapping is tidy. Jia and yi take wood, bing and ding fire, wu and ji earth, geng and xin metal, ren and gui water; the first of each pair is male, the second female. The branches become animals: rat, ox, tiger, rabbit, dragon, snake, horse, sheep, monkey, rooster, dog, pig.
2
So "Wood Rat" is "jia-zi". The words change, the number does not. Learn this one rule and the two systems read straight across, with no table.
What a rabjung is
A sixty-year cycle, in Tibetan rab byung, usually written rabjung and sometimes rabjung. The first began in 1027; this is the seventeenth. In speech nobody says "the seventeenth rabjung" — "Fire Horse year" or "Iron Ox year" is enough.
Iron and metal are the same thing. In spoken Tibetan, especially in Kham, metal is usually said as "iron". Iron Ox = Metal Ox = ji-chou — not three different years.
One inconvenience: "Fire Horse year" alone is ambiguous, since there are two in every sixty. That is why dates in old documents are often pinned by how long a named person held office. Not vagueness in the record — a property of the notation.
Conversion is never pure arithmetic
"Fire Horse year" will not yield a CE year on its own — there are two in each cycle. You need either the rabjung number or the context: who was in office, when a monastery was built. So dating an old document is half calculation and half history.
08 · II · THE START OF THE MONTH
The fifteenth is always full moon
Both calendars run their months on the moon, but they disagree on one fundamental convention: which day opens the month. That single choice keeps the two permanently out of step.
Chinese: counting from the new moon
Day one is the new moon — the night nothing is visible.
The full moon falls on the fifteenth or the sixteenth, not fixed.
So the moon on the Chinese fifteenth may still be a little short of full. "Roundest on the sixteenth" is not consolation; the rule allows it.
Tibetan: counting back from the full moon
The fifteenth is the full moon, fixed there.
The new moon falls on the thirtieth or on the first, not fixed.
So by the rule, the Tibetan fifteenth is always a full moon. The two calendars nailed the start of the month to two different events.
| Phase | Chinese | Tibetan |
|---|---|---|
| New moon | 1st, fixed | 30th or 1st |
| First quarter | 7th–8th | 7th–8th |
| Full moon | 15th or 16th | 15th, fixed |
| Last quarter | 22nd–23rd | 22nd–23rd |
Where the one-day gap comes from
Shift the start of the month by a day and every date in it shifts too. Which is why Tibetan New Year and the Spring Festival sometimes coincide and sometimes fall a day apart. The day is not an error in either calculation; the two fixed "the start of the month" on different events — one on the night the moon is born, the other on the night it is fullest.
One thing not to overstate. "The full moon is fixed at the fifteenth" is the rule; in practice, in a very few months the full moon lands on the fourteenth or the sixteenth. A full moon off the fifteenth in a given year is not a misprint.
A test you can run yourself
Take one month and look up the fifteenth in both calendars; see which Gregorian dates they land on. A day apart means the two started that month a day apart. No instruments needed — two calendars side by side will do it.
09 · II · LEAP MONTHS
A month apart, because the leaps differ
A day apart is a quarrel about the start of the month; a month apart is a quarrel about leap months. Both insert a leap month in a month with no mid-term, but they judge the sun differently — so the month they double is not always the same one.
Chinese: true solar terms
Seven leap months in nineteen years.
Uses true solar terms — the sun's actual path. Earth's orbit is an ellipse and its speed varies, so the gaps between mid-terms are unequal.
Which month gets doubled depends on where the sun actually is that year.
Tibetan: mean solar terms
About one leap month every thirty-two and a half months; twenty-four in sixty-five years.
Uses mean solar terms — the year divided into twenty-four equal parts.
Equal division is simple, but it runs slightly off the real sun, so the doubled month need not be the one the Chinese calendar chooses.
| Difference | Cause |
|---|---|
| Same day | Leap month and new-moon moment both coincide |
| 1 day | Different start-of-month convention, plus omitted and repeated days |
| 1 month | One inserts a leap month and the other does not; or both do, in different months |
| 1 month + 1 day | Both of the above at once |
The two leap rates are almost identical
Seven in nineteen years works out to one leap month every thirty-three and a half months; twenty-four in sixty-five years works out to the same.
So the difference is not how often a leap month comes, but which month is judged to be the leap one: one reads the sun's true position, the other an evenly divided one.
So the difference is not how often a leap month comes, but which month is judged to be the leap one: one reads the sun's true position, the other an evenly divided one.
So "Tibetan New Year is always a month behind the Spring Festival" is wrong, and "they always coincide" is wrong too. Four cases take turns. There is no fixed cycle.
A claim that circulates online does not hold. "A three-year cycle: same day, then a day apart, then a month apart" — it explains some years but it is not a rule. By the Tibetan astronomical authorities, it is the four cases above.
10 · II · OMITTED AND REPEATED DAYS
Dates skip, and sometimes repeat
Unique to the Tibetan calendar, and the easiest place to think you have misread: a month with no third day, or two fourth days in a row.
1
Where the gap is squeezed out. A synodic month is 29.53058 days, but the system assigns thirty whole "lunar days" to a month. Whole numbers cannot match that decimal, so the sequence must be adjusted: the day that will not fit is omitted, and the day that repeats is counted twice.
2
Omissions outnumber repetitions. Most months omit one or two days, fourteen or fifteen in a year; repeated days run to five or six at most. More days disappear than come back — because the real lunar period is shorter than thirty.
3
The "auspicious month". A month with neither an omission nor a repetition is called auspicious. Some years' almanacs mark them, and weddings and ground-breaking get scheduled into them.
4
Long and short months follow. A month with one omission and one repetition, or with two omissions, has 29 days and is short; the rest have thirty and are long.
The Gregorian way
Leap a day
The remainder is small, about six hours a year, so it takes four years to make a day — one correction every four years.
The Chinese way
Leap a month
The remainder is large, about eleven days a year, so two or three years make a whole month — add a whole month.
The Tibetan way
Drop a day
The remainder sits at the scale of the month, under a day each month — so it can only be adjusted a day at a time.
How much is it. Thirty lunar days against a real synodic month of 29.53058 days — about 0.47 of a day per month. Half a day is exactly the scale at which a date must be counted twice or skipped once.
So omissions and repetitions are not exceptions but routine, in any month. Over a year, fourteen or fifteen days are omitted and five or six at most are repeated.
One practical consequence
A Tibetan date cannot be counted as "the nth day". "The eighth" means the eighth in the sequence of dates; where that lands on the Gregorian calendar depends on that year's almanac. So anything that must match a real day — meeting someone, booking a car, catching a ceremony — goes by the almanac.
Of the three calendars, only this one can make a date not exist, or exist twice. Not a slip: force a real number of days into a calendar of whole dates and something has to give.
11 · III · TIBETAN FESTIVALS
A Tibetan year, and where its festivals fall
Tibetan festivals are fixed to a month and a day, which is why their Gregorian dates move every year. Below, in Tibetan month order, with no Gregorian dates.
1st month
day 1
day 1
Losar, Tibetan New Year. From the first to the fifteenth: visiting, prayer flags, the chemar offering box. The heaviest festival in the Tibetan world.
3rd month
day 15
day 15
Kalachakra festival. Tied to the Kalachakra Tantra; some monasteries hold ceremonies. A reminder of how directly the calendar descends from that text.
4th month
day 15
day 15
Saga Dawa. Marks the Buddha's birth, enlightenment and passing — all three on one day. A day for good deeds, for releasing animals, for going without meat.
6th month end
7th month start
7th month start
Shoton. Strongest around Lhasa: the great thangka unveiled at Drepung, opera in the Norbulingka. The name means "yoghurt banquet".
Before
the harvest
the harvest
Ongkor. A procession around the fields for a good yield. The date is not fixed — it follows the ripening of the crop, a survival of the phenological layer.
8th month
The bathing festival. For seven nights, by tradition, the star of the departing mountain is visible and the river is at its cleanest; people bathe in it. About a week long.
10th month
day 25
day 25
The butter-lamp festival. The anniversary of Tsongkhapa's death. Lamps go up on monastery roofs and house roofs; at night the whole hillside is points of light.
12th month
day 29
day 29
Guthuk. The new year's eve meal is a noodle soup with symbolic objects hidden in the dumplings; afterwards a rite drives the year's bad luck out of the door.
Why Ongkor has no fixed date
It is not set to a Tibetan month and day but to the crop. The barley has to be ripe, so the same festival can fall ten days apart in two neighbouring counties. This is the phenological layer alive — the oldest part of the calendar, visible now only in festivals like this one.
Shoton is not one festival across Tibet. It is centred on Lhasa; the Drepung unveiling and the Norbulingka opera are Lhasa's way of keeping it. Other Tibetan regions may mark nothing of the kind. Same name, different observance — a festival is not only its name.
12 · III · CHINESE FESTIVALS
Chinese festivals run on two frames
Most major Chinese festivals are fixed by the moon; two are fixed by the sun. That dividing line decides whether they drift on the Gregorian calendar.
| Festival | Fixed at | By |
|---|---|---|
| Spring Festival | 1st day, 1st month | moon (new) |
| Lantern Festival | 15th day, 1st month | moon (full) |
| Clear and Bright | solar term, 4–6 April | sun |
| Dragon Boat | 5th day, 5th month | moon |
| Qixi | 7th day, 7th month | moon |
| Ghost Festival | 15th day, 7th month | moon (full) |
| Mid-Autumn | 15th day, 8th month | moon (full) |
| Double Ninth | 9th day, 9th month | moon |
| Winter Solstice | solar term, 21–23 December | sun |
One line divides them: festivals fixed by the moon drift on the Gregorian calendar every year; festivals fixed by the sun barely move. Clear and Bright and the winter solstice land on the same few days each year; the Spring Festival can shift by a month. That is the whole reason.
New moon and full moon, what they look like
On the first of the month the moon is invisible; on the fifteenth it is at its roundest. From new to full is about 14.77 days — slightly less than half a month, which is why the full moon can land on the fifteenth or the sixteenth. "Roundest on the sixteenth" is allowed by the rule, not a consolation.
Why these festivals sit on the fifteenth
The Lantern Festival needs lanterns, the Ghost Festival needs lamps, Mid-Autumn needs a moon to look at — all of them need a full moon. So they landed on the same day without conferring. A festival date is not picked at random; it follows what the day is for.
13 · III · WESTERN FESTIVALS
Western festivals use three methods
The Gregorian calendar is purely solar, yet Western festivals are not all fixed to Gregorian dates. Three methods coexist — and the most complicated of them runs on the moon.
1 · Fixed date
The date holds
Christmas (25 December), New Year (1 January), Valentine's (14 February). The date is written into the calendar; the weekday moves every year.
2 · By weekday
The weekday holds
Thanksgiving (fourth Thursday in November), Mother's Day (second Sunday in May), Labor Day in the US (first Monday in September). The weekday is fixed and the date moves — to manufacture a long weekend.
3 · By the moon
Both move
Easter. The rule: the first Sunday after the first full moon following the spring equinox. Neither date nor weekday is fixed.
| Festival | Fixed by | What is stable |
|---|---|---|
| New Year | 1 January | the date |
| Christmas | 25 December | the date |
| Mother's Day | second Sunday in May | the weekday |
| Thanksgiving | fourth Thursday in November | the weekday |
| Easter | first Sunday after the first full moon after the equinox | neither |
Why Easter is so convoluted
Three things sit inside that rule: the equinox (sun), the full moon (moon), Sunday (weekday). Put together, Easter falls between 22 March and 25 April — a spread of more than a month. It follows the rule laid down at Nicaea in 325, when the underlying thinking was still lunisolar.
The most telling detail: a purely solar calendar whose biggest festival has to be computed from the moon. The reason is not astronomical but historical — the rule was written too early, and later reform left it alone.
Three methods, three kinds of movement. Fixed date: the date holds, the weekday moves. By weekday: the weekday holds, the date moves. By the moon: both move. See which method a festival uses and you know what will hold.
14 · CLOSING
One table, three calendars side by side
| Gregorian | Chinese | Tibetan | |
|---|---|---|---|
| Anchored to | the sun | sun + moon | sun + moon |
| Start of month | by convention | the new moon | full moon at 15, counted back |
| A month | 28–31 days | 29 or 30 days | 29 or 30 days |
| A year | 365 or 366 days | 354; 383–385 in a leap year | 354; 383–385 in a leap year |
| How it leaps | one day | 7 in 19 years, true terms | about 1 in 32.5 months, mean terms |
| Unique feature | — | the 24 solar terms | omitted and repeated days |
1
The disagreement sits in two places only. Where the month starts, and how a leap month is added. Get those two clear and every remaining difference in dates can be worked out — no year-by-year conversion table needed.
2
Chinese and Tibetan look alike because they share an origin. They compute differently because after 1027 they each went their own way for a thousand years. "Similar" and "the same" are two different things.
3
For a traveller, the one useful sentence is: Tibetan festivals move against the Gregorian calendar every year. Do not hold a date in your head. Check that year's almanac rather than working it out.
Why the text carries no dates
Rules do not expire; dates do. So the text gives the rules only — a rule is a tool, a date is only a reference. The table at the back is a single snapshot: it names its two years, and once those years are past it has to be redone. Tickets, opening hours and driving times are left out of this series for the same reason.
Leap days, leap months, omitted days and repeated days — different names for one job: nailing three cycles that refuse to divide evenly onto a grid made of paper.
October 2026
Samantha
Compiled from public sources: the explanatory material and published interviews of the astronomical calendar institute at the Tibetan hospital in Lhasa; studies of the Kalachakra and of the Tibetan calendar; the New Tang History and the Old Tang History, chapters on the Tibetans; public explanations of the Chinese calendar and of the 24 solar terms from the National Time Service Centre and the Purple Mountain Observatory; and the literature on the Gregorian reform, including the 1582 papal bull and the dates on which various states adopted the new calendar. Where scholarship holds two views, the text says so or marks one as the customary account; the table at the back is compiled from published calendar material and covers only the two years it names.
15 · APPENDIX · ONE AXIS
Fifteen Months, Three Calendars on One Axis
The left column is the Gregorian month; the next three give the Tibetan, Chinese and Western festivals that fall in it. Only the day is written — the month is already at the left end of the row.
| Gregorian | Tibetan | Chinese | Western |
|---|---|---|---|
| 2026.10 | — | 1 National Day · 18 Double Ninth | 31 Halloween |
| 2026.11 | 1 Lhabab Duchen | — | 26 Thanksgiving |
| 2026.12 | 3 Ganden Ngamchoe | — | 25 Christmas |
| 2027.01 | — | 1 New Year's Day · 15 Laba | 1 New Year |
| 2027.02 | 6 Guthuk · 7 Losar 20 Butter Lamp Festival | 5 New Year's Eve · 6 Spring Festival 20 Lantern Festival | 14 Valentine's Day |
| 2027.03 | — | — | 28 Easter |
| 2027.04 | — | 5 Qingming | — |
| 2027.05 | — | 1 Labour Day | 9 Mother's Day |
| 2027.06 | 18 Saga Dawa | 9 Dragon Boat | 20 Father's Day |
| 2027.07 | — | — | 4 Independence Day (US) |
| 2027.08 | 31 Shoton | 8 Qixi · 16 Ghost Festival | — |
| 2027.09 | — | 15 Mid-Autumn | — |
| 2027.10 | 29 Kongpo New Year | 1 National Day · 8 Double Ninth | 31 Halloween |
| 2027.11 | 13 Palden Lhamo 23 Ganden Ngamchoe | — | 25 Thanksgiving |
| 2027.12 | — | — | 25 Christmas |
How to read the table
The Tibetan column comes from published calendar material. Tibetan months contain omitted and repeated days, so one observance can land a day apart in different sources; to plan around one, use that year's almanac as issued in Lhasa. The Chinese column mixes lunar dates with three fixed Gregorian ones (New Year's Day, Labour Day, National Day); Qingming is a solar term, not a lunar date. The Western column keeps only the most-asked: Thanksgiving is American, the fourth Thursday in November.
Ongkor will not fit. Each village sets it by when its grain ripens. Shigatse, Nyingchi and Ngari also keep their own new year; the table gives Lhasa's Losar only. A festival each village sets for itself defeats any single table.
On the dates. Every date in this notebook is a rule, not a lookup: the pages say how a year is assembled, not what any particular year contains. The one exception is the last table, and it is labelled with the two years it covers.
On the sources. The 29.53-day synodic month, the 365.2422-day tropical year and the 1582 reform are standard astronomy and standard history. The Tibetan material follows the Phugpa tradition as set out in the calendars printed in Kham and in the standard Chinese-language surveys of the Tibetan calendar.