Leap Month Calculator
Check whether a lunar month is normal or leap, and find leap-month date ranges by year.
Category: Date & Time
When to use?
Use it to check whether a given year has a lunar leap month and, if so, the corresponding solar (Gregorian) date range — useful for traditional events held in a leap month.
How to use
- Enter the year or a specific date to look up.
- When converting a date, check whether it is a normal month or a leap month.
- For a yearly lookup, see whether the year has a leap month and its solar date range.
Input Explanation
Select the solar date to calculate, or the year to look up (range 1900–2050).
Calculation Basis
Using a built-in 1900–2050 lunar new-moon table, it back-calculates the presence of a leap month and monthly day counts to find the corresponding solar range.
Usage Examples
- Check for a leap month - Check whether a year has a leap month when choosing an auspicious day for a move, reburial, or wedding.
- Check a lunar birthday - Check whether a parent's lunar birthday falls in a leap month for a given year.
Examples
- Look up 2023 → has a leap 2nd month (solar Mar 22 – Apr 19, 2023)
- Look up 2025 → has a leap 6th month (solar Jul 25 – Aug 22, 2025)
Cautions
- This tool provides lunar data for 1900–2050. Years outside this range cannot be looked up.
- It follows standard civil lunar data, so astronomical observation differences may cause a one-day variance.
Guides
The lunar calendar and leap months
The lunar calendar sets a month by the moon's phases, so to bridge the roughly 11-day yearly gap with the solar year, an extra month (leap month) is inserted about once every three years.
Auspicious-day customs
In Korean tradition a leap month was believed to be free of misfortune, a month that escapes heaven's notice. Important events like reburials, preparing burial clothes, and weddings were often held during it.
FAQ
What is a leap month?
A lunar year is about 354 days. To correct the gap with the solar year (365.24 days), an extra month is inserted roughly once every three years — that is a leap month.
Does a leap month occur every year?
No. On average it occurs 7 times in 19 years (about once every 2.7 years).
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