Gregorian dates, lunar dates and leap months

Check which calendar the record uses

For a Gregorian date, leave Korean lunar calendar unchecked. For an original Korean lunar birth date, select it and enter the lunar numbers. If you already converted a date to Gregorian, do not select lunar again: that would convert it a second time.

Korean lunar 2024-01-01 converts to Gregorian 2024-02-10. The result summary shows both dates so that you can check the conversion separately from the rest of the reading.

A leap month is a separate month

In a leap year of the lunar calendar, a regular month and a leap month with the same number refer to different periods. Korean lunar 2025 regular month 6 day 1 differs from leap month 6 day 1; the latter converts to Gregorian 2025-07-25.

Select the leap-month option only when the original record specifies it. A leap month that does not occur in the selected year, or a day that does not exist in that month, produces an error rather than a guessed date.

Lunar February can have a day 30

A Gregorian date picker cannot accept February 30. Selecting the lunar option therefore uses a YYYY-MM-DD text field. Each lunar month can have 29 or 30 days depending on the year; validation must use the selected calendar.

Korean lunar 2024-02-30 converts to Gregorian 2024-04-08. A date that is invalid in the Gregorian calendar is not necessarily an invalid lunar record.

Conversion comes before chart calculation

First the Korean lunar date is converted to Gregorian. Then the birthplace and recorded local time determine the historical time-zone offset and local mean solar-time correction. Solar terms and the corrected day and hour are used for the pillars. A lunar month number is not directly substituted for the month pillar.

Chinese, Vietnamese and other lunar calendars can differ from the Korean calendar. For records in those calendars, confirm the corresponding Gregorian date and enter that date instead. Korean lunar conversion uses the browser’s Dangi calendar data.

Sources and references

• Korea Astronomy and Space Science Institute · 2025 calendar ↗