How to use
Pick a conversion at the top.
- Solar → Lunar: enter a solar (Gregorian) date to see the lunar date, whether it falls in a leap month, and the year’s name and zodiac animal. Today’s date is filled in to start. Below, a calendar of that month shows the lunar day in small type under each date. Tap a date in the calendar or use the ‹ › buttons to change the month.
- Lunar → Solar: enter the lunar year, month and day, and tick “Leap month” if it’s a leap month. You’ll be told if that year has no such leap month, or if you enter the 30th in a month that only has 29 days. Once you enter a year, you’ll also see which month that year’s leap month follows.
- Lunar birthday: enter the month and day of the lunar birthday and a year to see which solar date the birthday falls on that year, plus the dates for the next 10 years.
How the Korean lunar calendar works
A lunar month starts on the day of the new moon (the moment the Moon and Sun line up) and ends the day before the next new moon. Because the Moon’s cycle is about 29.5 days, a lunar month has either 29 days (short month) or 30 days (long month), and which months are long changes from year to year.
Twelve lunar months add up to about 354 days, roughly 11 days shorter than a solar year. To keep the calendar in step with the seasons, a leap month is added about 7 times every 19 years. A leap month takes the number of the month just before it, as in “leap month 4”. For example, 2020 had a leap month 4, 2023 a leap month 2 and 2025 a leap month 6; 2026 has no leap month, and the next one is leap month 5 in 2028.
The Korean lunar calendar sets the day of each new moon in Korea Standard Time (based on 135°E, UTC+9). The Chinese lunar calendar uses China Standard Time (UTC+8), so in months where the new moon falls between midnight and 1 a.m. Korean time, day 1 of the month differs by one day between the two countries. That’s why Seollal, Chuseok or a lunar birthday is sometimes one day off from a Chinese calendar. This calculator follows the Korean lunar calendar published by KASI.
Year names (the sexagenary cycle, ganji) repeat every 60 years, and in this calculator they change on Seollal. 2026 is the Byeong-o year (丙午), the Year of the Horse.
Lunar birthdays
The same lunar date lands on a different solar date every year. Chuseok (day 15 of lunar month 8), for example, was on September 17 in 2024, October 6 in 2025 and September 25 in 2026. That’s why a lunar birthday needs to be looked up again each year.
When the birthday doesn’t exist in a given year, this calculator uses these rules:
- Leap-month birthday: counted in the regular month with the same number. If the year has that same leap month, the leap-month date is shown too.
- Birthday on the 30th: if that month only has 29 days that year, the 29th is used.
The year is the lunar year. Birthdays in lunar months 11 and 12 can fall in January or February of the next solar year. For example, day 20 of lunar month 12 of 2026 is January 27, 2027.
Supported range and data source
Supported dates run from January 31, 1900 to December 31, 2050 (solar), which is lunar 1900, month 1, day 1 to lunar 2050, month 11, day 18. KASI’s lunar–solar converter also goes up to December 31, 2050.
Conversion runs in your browser using korean-lunar-calendar (MIT License), an open-source library that bundles a KASI-based conversion table. The dates you enter aren’t sent to any server. On September 24, 2026, every Seollal in this range (151), the start date and length of every leap month (56), every Chuseok from 2000 to 2049 and 100 random solar dates were checked against KASI’s lunar–solar converter, and all of them matched. For an official check, use KASI’s lunar–solar converter (in Korean).