What is a Leap Month (閏月) and Does it Affect My Birthday?
A leap month (閏月, rùn yuè) is an extra month inserted into the Chinese lunar calendar every 2 to 3 years to keep it aligned with the seasons. It is the lunar calendar's equivalent of the Gregorian leap day — but instead of adding a single day, an entire extra month is added.
Why a leap month is needed
A standard Chinese lunar year has 12 months totalling around 354 days — about 11 days fewer than the solar year of 365.25 days. Without correction, the calendar would drift steadily backward through the seasons. After just 3 years the drift would exceed a full month; after 16 years, the Lunar New Year would fall in autumn instead of late winter.
The solution, worked out by Chinese astronomers over two millennia ago, is to add an extra month in certain years. Over a 19-year cycle (called the Metonic cycle), exactly 7 leap months are inserted. This keeps the average lunar year in close alignment with the solar year.
Which month is repeated?
Unlike the Gregorian leap day, which always falls on 29 February, a Chinese leap month can fall after any of the 12 regular months. The specific month that is repeated is determined by astronomical rules — primarily by which month contains no major solar term (中氣, zhōng qì). The repeated month takes the same number as the month it follows, preceded by the word "Leap" (閏). For example:
- Leap Month 4 (閏四月) — follows the 4th lunar month
- Leap Month 6 (閏六月) — follows the 6th lunar month
- Leap Month 11 (閏十一月) — follows the 11th lunar month
Recent and upcoming leap months: 閏四月 occurred in 2020; 閏二月 in 2023; 閏六月 in 2025; 閏四月 again in 2028.
How a leap month affects your birthday
If your birthday falls in a regular month that happens to also have a leap month that year, your birthday is celebrated in the regular month as usual. The leap month that follows it is simply an additional month — it does not replace yours.
If you were born during a leap month (which is rare — it only happens once every 2–3 years for any given person's birth month), then in most years your birthday will be observed in the regular version of that month. The "true" leap month birthday only recurs in years when the same leap month appears again — which may be decades apart.
Our Lunar Calendar Converter handles all of this automatically. It knows which years have leap months and which months are repeated, and calculates the correct Gregorian date for each year without any manual lookup.