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Lunar · Gregorian converter
Converts dates while distinguishing leap months and long and short months. It also shows the day's iljin and whether it's a Son-eomneun-nal. Works from 1900 to 2050.
Son-eomneun-nal in this lunar month
Days whose lunar date ends in 9 or 0. The full monthly calendar is in the Son-eomneun-nal hub.
Look at your Saju from your lunar birthday
Enter the converted Gregorian date in the Manseryeok calculator to get your Eight Characters. In the app, just enter your birthday to get started.
Get the app for iPhone & AndroidWhere the lunar calendar gets confusing
Leap months
Twelve lunar months come to about 354 days, roughly 11 days shorter than a Gregorian year. Left alone, within a few years Seollal would land in summer. So seven times in 19 years a month is repeated, making a year of thirteen months. This added month is the leap month.
Leap month 5 is a second 5th month that comes after the 5th month. That's why, when you give a lunar date, you need to say whether or not it's in a leap month. It's also why this converter has a separate leap-month checkbox when you enter a lunar date.
Long and short months
A lunar month follows the moon's waxing and waning cycle of about 29.53 days. Since that doesn't come out even, short months of 29 days and long months of 30 days are mixed. So there's no 31st in the lunar calendar. And some months have no 30th.
That's why people whose lunar birthday is on the 30th find their birthday missing in some years.
Why your lunar birthday moves every year
The lunar calendar follows the moon, and the Gregorian calendar follows the sun. The two cycles don't divide evenly into each other, so the same lunar date moves back and forth by ten days or so on the Gregorian calendar each year. In a year with a leap month, the gap grows even larger.
Is Saju read using the lunar calendar?
No. Saju is based on the solar terms — the position of the sun, neither the lunar nor the Gregorian calendar. So in Saju the year changes not at Seollal but at Ipchun, and the month changes not on the 1st of the lunar month but at a solar term. The lunar calendar is needed when looking at customs set by lunar dates, like Son-eomneun-nal.
The Korean lunar calendar and the Chinese lunar calendar sometimes differ
The lunar calendar takes as the first day of the month the day containing the new moon (sak 朔) — the moment the moon lines up in the same direction as the sun. Depending on which country's clock you read that moment by, the date can differ by a day. Korea and China are one hour apart, after all.
For example, Seollal 2027 falls on February 7 by the Korean lunar calendar, but on February 6 by the Chinese lunar calendar. Comparing all of 1900–2050, there are 427 days on which the Son-eomneun-nal result differs. This converter uses Korea Standard Time. More details are in Why manseryeok apps give different results.
How it's calculated
This data is built from new moons in Korea Standard Time and the no-zhongqi leap-month rule (a month without a mid-month solar term becomes the leap month). It covers 1900–2050, and all 55,002 days from 1900 to 2050 were round-trip verified Gregorian → lunar → Gregorian, confirming there were no mismatches. The app's manseryeok was also cross-checked against the lunar–Gregorian data published by the Korea Astronomy and Space Science Institute (KASI).
FAQ
What is a leap month?
Twelve lunar months come to about 354 days, roughly 11 days shorter than a Gregorian year. As this gap builds up the seasons drift, so seven times in 19 years a month is repeated, making a year of thirteen months. This added month is the leap month. For example, leap month 5 is a second 5th month that comes after the 5th month.
Why does my lunar birthday fall on a different Gregorian date every year?
Because the lunar calendar follows the moon's phases, while the Gregorian calendar follows the Earth's orbit around the sun. The two cycles don't divide evenly into each other, so the same lunar date moves back and forth by ten days or so on the Gregorian calendar each year. In a year with a leap month, the gap grows even larger.
Is there a 31st in the lunar calendar?
No. A lunar month follows the moon's waxing and waning cycle of about 29.53 days, so it's either a short month of 29 days or a long month of 30 days. That's why the 31st of a lunar month doesn't exist.
What range of years can be converted?
From 1900 to 2050. We round-trip verified all 55,002 days from 1900 to 2050 — Gregorian to lunar, then lunar back to Gregorian — and confirmed there were no mismatches.