Lunar birthday
Enter the lunar date you keep and see the Gregorian date it falls on for the next fifteen years. Explains the eleven-day drift and what happens to a leap-month birthday.
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Enter the lunar date you keep, and see when it falls.
The next fifteen years
| Year | Gregorian date | Weekday | Lunar |
|---|
Dates are civil days at UTC+8, which is where the calendar is defined.
Why it moves, and by how much
A lunar year of twelve months is about 354 days. A solar year is about 365¼. So a birthday kept by the lunar calendar arrives about eleven days earlier each year — until a leap month is inserted, and it jumps back about nineteen days later.
Over any nineteen years the two calendars nearly agree again: 19 solar years are 6,939.6 days, and 235 lunar months are 6,939.7 days. The gap is about two hours. That is the Metonic cycle, and it is why your lunar birthday tends to land within a day or two of the same Gregorian date once every nineteen years — and why seven of every nineteen lunar years carry a leap month.
It is a near-coincidence, not an identity. Two hours a cycle accumulates, so the nineteen-year return drifts by a day every few cycles. The table above is computed date by date rather than by adding nineteen.
The months are 29 or 30 days, and which is not fixed
There is no such thing as a lunar month that is always 30 days. The length depends on the interval between two new moons, which varies from about 29.27 to about 29.83 days with the Moon’s elliptical orbit.
So 三十 — the 30th — does not exist every year. If you were born on the 30th of a month, some years simply have no such date. The table skips those years rather than silently moving you to the 29th or the 1st of the next month, because which of those a family observes is a family’s decision and not a calculation.
Leap-month birthdays
If you were born in a leap month — 閏六月, say — the same leap month recurs only every few years, and in some cases not for decades. 閏六月 falls in 1979, 1987, 2017, 2025 and then not again until 2036.
Tick the leap box and the table shows the ordinary month in years that have no such leap month, marking each of those rows. Again, that is not the tradition deciding for you: most families keep the ordinary month, some observe nothing that year, and a few keep the day the leap month would have fallen on. The tool shows a date; you choose what to do with it.
Which date is “your” birthday
Two people born on the same day can keep different birthdays for life, and both are right:
- The lunar date is what a Chinese, Taiwanese or Hong Kong family register would have recorded before the 20th century, and what many households still use for elders’ birthdays, for 做壽 and for ancestral rites.
- The Gregorian date is what every official document uses now.
If you know one and want the other, the lunar calendar converter turns either into the other for any date between 1900 and 2100.
What this covers
The table runs from 1900 to 2100 and is generated from astronomical computation, then checked against published Lunar New Year dates and leap months before it is allowed to ship. Dates are civil days at UTC+8, which is where the calendar is defined.
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