How to use
Pick one of three options under “Conversion”.
- Solar → Lunar: enter a “Solar (Gregorian) date” to get the lunar date. The result also tells you whether that lunar month runs to 30 days (a long month) or 29 (a short month), and gives the “Year name (zodiac)” for that year. Today’s date is filled in to start. Below the result is a calendar of the month, with the lunar day in small type under each date. On the day a new lunar month begins, the cell shows the month instead of a number, as in “M1”. Tap a date, or move between months with the ‹ › buttons, and the calculator converts that date.
- Lunar → Solar: choose the “Lunar year”, the month and the day, and tick “Leap month” if the date falls in a leap month. A note under the year field says which month that year’s leap month follows, or that the year has none. If you pick a leap month the year doesn’t have, or day 30 in a month that stops at 29, the calculator tells you why it can’t convert.
- Lunar birthday: choose a “Year” and the month and day of the lunar birthday. You get the solar date of the birthday in that year and a table of dates for the “Next 10 years”. If the person was born in a leap month, tick “Born in a leap month”.
Solar dates of Seollal and Chuseok
Seollal, Korea’s Lunar New Year, is day 1 of lunar month 1. Chuseok, the autumn harvest holiday, is day 15 of lunar month 8. The lunar dates never change, but the solar dates move every year. Even within the five years below, the earliest and latest dates are three weeks apart.
| Year | Seollal (lunar month 1, day 1) | Chuseok (lunar month 8, day 15) |
|---|---|---|
| 2024 | February 10 | September 17 |
| 2025 | January 29 | October 6 |
| 2026 | February 17 | September 25 |
| 2027 | February 7 | September 15 |
| 2028 | January 27 | October 3 |
For any other year, go to Lunar → Solar and enter the year with month 1, day 1 or month 8, day 15. Any other day you keep by the lunar calendar can be looked up the same way.
Working out a lunar birthday
A lunar birthday falls on a different solar date each year, so it has to be looked up again every year. Lunar birthday does that for ten years at once. When the birthday’s date doesn’t exist in a given year, the calculator applies the rules below and adds a note to the result saying so.
- Born in a leap month: a leap month only comes around once every few years, so the birthday is counted in the regular month with the same number (the ordinary, non-leap month). If you were born on day 10 of leap month 6, then in 2026, which has no leap month, your birthday is day 10 of lunar month 6, or July 23, 2026. When the year does have the same leap month, both dates are shown. In 2025, which had a leap month 6, you get day 10 of the regular month 6 (July 4) and day 10 of leap month 6 (August 3). Which one to celebrate is up to your family’s custom.
- Born on day 30: if the month only has 29 days that year, the last day, the 29th, is used. Lunar month 2 of 2026 has 29 days, so a birthday on day 30 of month 2 becomes day 29, or April 16, 2026. In the table, these years are tagged “on the 29th”, and years where a leap month was swapped for the regular month are tagged “regular month”.
The “Year” is a lunar year. A birthday in lunar month 11 or 12 can fall in January or February of the following solar year. Enter 2026 as the year with a birthday on day 20 of month 12 and the result is January 27, 2027.
How the Korean lunar calendar is set
A lunar month begins on the day of the new moon, the moment the Moon and the Sun line up in the same direction, and ends the day before the next one. The Moon’s cycle of phases takes about 29.5 days, so a lunar month has either 29 days (a short month) or 30 days (a long month), and which months are long changes from year to year.
Twelve lunar months come to about 354 days, roughly 11 days short of a solar year. To stop that gap from building up and pulling the calendar away from the seasons, a leap month is added about 7 times in every 19 years. A leap month takes the number of the month before it, as in “leap month 4”. There was a leap month 4 in 2020, a leap month 2 in 2023 and a leap month 6 in 2025. Neither 2026 nor 2027 has one, and the next is leap month 5 in 2028.
The Korean lunar calendar fixes 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 a month when the new moon falls between midnight and 1 a.m. Korean time, day 1 of the lunar month is a day apart in the two countries. That is why Seollal, Chuseok or a lunar birthday is sometimes one day off from a Chinese calendar. This calculator follows the Korean lunar calendar as given by the lunar–solar converter of the Korea Astronomy and Space Science Institute (KASI).
Year names and zodiac animals
“Year name (zodiac)” is the name of the year (ganji) with its zodiac animal. The same name comes back every 60 years, and 2026 is the Byeong-o year (丙午), the Year of the Horse. In this calculator the year name changes on Seollal, the same as the lunar year name in KASI’s lunar–solar converter. Lunar → Solar shows the name of the lunar year you entered. Solar → Lunar shows the name of the year that the converted lunar date belongs to.
Supported range and how it was checked
Supported dates run from January 31, 1900 to December 31, 2050 in the solar calendar, which is day 1 of lunar month 1 of 1900 to day 18 of lunar month 11 of 2050. KASI’s lunar–solar converter also covers dates up to December 31, 2050.
The calculator doesn’t query KASI when it converts. It uses korean-lunar-calendar (MIT License), an open-source library that carries a KASI-based conversion table. 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 compared with the results of KASI’s converter, and all of them matched. If you need an official confirmation, use KASI’s lunar–solar converter (in Korean).