Home › Notes › Finding your lunar birthday

Your lunar birthday
on the Gregorian calendar

Calculation · 2026.08.30 · 6 min read · Updated 2026.10.02 · Updated 2026-10-10

Why is my lunar birthday on a different date every year?

Because a lunar year is a little over ten days shorter than a Gregorian year. Lunar months follow the moon's cycle of waxing and waning (about 29.53 days), so twelve of them add up to about 354 days. That's eleven days short of the Gregorian 365.

So when you carry a lunar birthday over to the Gregorian calendar, it moves about ten days earlier each year, then shifts back about a month in a year with a leap month. Watching how Chuseok (the 15th day of the 8th lunar month) moves makes it clear at a glance.

You can see the pattern. It moves 10–11 days earlier each year, then jumps back nearly a month in a year with a leap month. That's how the lunar calendar keeps its dates from drifting away from the seasons.

How do I find my lunar birthday?

Just convert your Gregorian birth date to the lunar calendar. Conversely, if you only know your lunar birthday, converting it tells you which Gregorian date it falls on this year. Here are the steps.

1. Check whether the birthday on your resident registration is Gregorian or lunar. In the past, many births were registered by the lunar date, so asking your parents is the surest way.
2. If it's Gregorian, convert that date to the lunar calendar. That's your lunar birthday.
3. If it's lunar, convert it to this year's Gregorian date. It changes every year, so you'll need to check again each year.
4. Check whether the result is marked as a leap month (yun). A leap-month birthday needs separate handling.

You can convert it right away with the Lunar–Gregorian converter. It covers 1900 to 2050, and the date you enter is processed only within your browser.

What is a leap month, and when does it come?

It's an extra month inserted into the lunar calendar. The eleven-day gap we saw above adds up to a month in about 3 years, and at that point the same month is added once more — so the 5th month, say, comes around twice: the 5th month and the leap 5th month.

It comes seven times in 19 years — in other words, once every 2–3 years. Which month becomes the leap month depends on how the solar terms fall.

There's no leap month in 2027. The twelve lunar months pass as usual. The next leap month is the leap 5th month in 2028.

If I was born in a leap month, when do I celebrate?

A leap-month birthday comes back on its exact date only about once every 19 years. So most people do one of the following.

Celebrate in the regular month

The most common way. If you were born on the 10th day of the leap 5th month, you simply celebrate on the 10th day of the 5th month.

Fix it to the Gregorian date

Use the Gregorian date of the day you were born as your birthday. It's the same day every year, so it's easy to remember.

Use the leap month only when it comes around

It's rare, but some families celebrate in the leap month in the years when that leap month comes back.

There's no right or wrong here. It's up to each family.

What if my lunar birthday is the 30th and that year has no 30th?

Lunar months are a mix of months that end on the 29th (short months) and months that run to the 30th (long months). The moon's actual cycle is 29.53 days, so it doesn't divide evenly. That means someone born on the 30th of a lunar month has no birthday at all in some years.

The classic example is the 30th day of the 12th lunar month — Seotdal Geumeum, the last day of the lunar year.

In years without a 30th, the custom is to celebrate on the 29th. Ancestral memorial rites likewise follow the last day of the month.

What does the 2027 lunar calendar look like?

Here's the Gregorian date on which each lunar month of 2027 begins. If you have a lunar birthday, this gives you a rough idea of where it falls.

To get the Gregorian date, add the lunar day minus 1 to the month's start date. For lunar 3/20, that's April 7 + 19 days = April 26 (Mon). Son-eomneun-nal in 2027 are also set by lunar dates (the 9th, 10th, 19th, 20th, 29th and 30th), so you can roughly work them out from this table.

Should I enter the lunar date for a Saju reading?

The Gregorian date is the right one to enter. Saju is calculated by the solar terms, and since solar terms follow the sun's position, they move closely with the Gregorian calendar. If you enter a lunar date as-is, your month pillar can be entirely wrong.

If you only know your lunar birthday, convert it to Gregorian first and then enter it. And one more thing — if you also have your birth time, all Eight Characters get filled in. If you don't know your time, see How to find your birth time.