How to use it
- Birthday planner: enter a birth date in either calendar at the top to see the solar and lunar birthday dates, weekdays, countdowns, holiday or weekend overlaps and how many days off one day of leave gives you, for this year and the next two.
- Lunar birthday: choose the lunar month and day, and pick 'Leap month' if you were born in one. The start year defaults to this year.
- Results: a table of solar dates and weekdays from the start year for ten more years, with the next upcoming birthday and a countdown on top.
- Converter: the second tab turns a solar date into a lunar date and back. For a solar date it also shows the sexagenary year and day (for example 丙午年 甲子日).
- Your inputs stay in the page address, so 'Share this result' sends a link that opens the same table.
Why lunar birthdays move
A lunar month follows one cycle of the Moon, about 29.5 days, so months have 29 or 30 days and twelve of them add up to about 354 days. Because that is about 11 days shorter than a solar year, the same lunar date falls earlier on the solar calendar every year.
To keep the calendar in step with the seasons, a leap month is added about seven times every nineteen years. In those years a lunar birthday jumps back almost a month. Seollal, the lunar new year, fell on January 29 in 2025 and February 17 in 2026, and falls on February 7 in 2027 and January 27 in 2028.
Leap-month and day-30 birthdays
- Leap-month birthdays: leap months come every few years and in a different month each time (leap month 2 in 2023, leap month 6 in 2025). In years without one, the calculator uses the same day of the regular month, as is customary in Korea.
- Day-30 birthdays: if the month has only 29 days that year, the calculator uses day 29.
- Both adjustments are noted in the table. Families may keep birthdays differently, so treat the results as a guide.
Korean and Chinese lunar dates can differ
Both calendars follow the same Moon, but they divide days by different clocks: Korea uses Korea Standard Time (UTC+9) and China uses China Standard Time (UTC+8). When a new moon falls close to midnight, the two calendars can start the month on different days. If a Chinese calendar app shows a date one day off, this is usually why. This calculator follows the Korean (KASI) standard.
Range and sources
Conversions use korean-lunar-calendar, an open-source library of KASI's lunar tables, and cover lunar years 1000 to November 2050. Seollal and Chuseok for 2025–2030, Buddha's Birthday in 2026 and 2027, and the first days of the leap months in 2020, 2023 and 2025 were checked against published dates. See the Korean public holidays for 2026 and 2027.