Lunar Birthday for Saju: Solar or Lunar Date, and Leap Months

Many Korean, Chinese and Vietnamese families still keep birthdays on the lunar calendar. If your grandmother says you were born on "the 10th day of the 2nd month", that is a lunar date, and it is not the same day as 10 February. Saju charts are built from the calendar, so entering the right kind of date matters more than almost any other input. This guide explains which date to enter, what a leap month is, and how to check the date you were given.

Have the calculator open (free, no account): the Saju calculator has a Solar / Lunar switch under the birth date. You will use it in the checks below.

Solar date or lunar date: which one do you have?

Start by asking where your date came from.

A simple clue: a solar birthday falls on the same day every year on a normal calendar. A lunar birthday moves around, usually within a range of several weeks, because lunar months follow the moon.

If you have both, use the solar date from your official documents and treat the lunar date as a cross-check. The two should describe the same day.

How the calculator uses a lunar date

When you choose Lunar, the calculator converts your lunar date to its matching solar day, then builds the four pillars from that day exactly as it would for a solar entry. The result for the same birth is the same chart, as long as both dates describe the same day.

That means the choice of Solar or Lunar does not change the method. It only tells the calculator how to read the numbers you typed. Typing a lunar date with Solar selected is the most common way to get a chart for the wrong day, often a month or more away from the real one.

Two other things to know:

• The year you enter with a lunar date is the lunar year. A birth in the 12th lunar month of 2023 can fall in January or February 2024 on the solar calendar. For instance, the 20th day of the 12th lunar month of 2023 is 30 January 2024.
• The calculator rejects lunar dates that do not exist, such as a 30th day in a month that only has 29 days. If you get an error, check the day number with your family before guessing.

Leap months, explained

Twelve lunar months are about eleven days shorter than a solar year. To stay in step with the seasons, the lunar calendar adds an extra month roughly seven times every nineteen years. That extra month is a leap month (윤달, yundal, in Korean; 閏月 in Chinese), and it repeats the number of the month before it.

In 2023, for instance, there were two "2nd months": the regular one and a leap one. The 10th day of each falls on a different solar date:

A month apart, and a different month pillar. When you switch the calculator to Lunar, a leap-month checkbox appears. Tick it only if your family record says the birth was in the leap month. If you are not sure, run the chart both ways and see which solar date your documents agree with.

Lunar date, saju year and the zodiac animal

People with lunar birthdays often assume the saju year starts on Lunar New Year. In most saju and BaZi practice it does not. The year pillar changes at Ipchun (입춘, 立春), the solar term often translated as the "start of spring", which usually lands on 3, 4 or 5 February. Lunar New Year can fall a couple of weeks before or after that. Korean Zodiac Animals and Saju: Why Your Chart Year Can Differ lists the twelve animals by year and shows how to check which one applies to you.

So a lunar birthday in the first days of the lunar year can still carry the previous year's pillar, and a birth in the last lunar month can already carry the new one. Month pillars work the same way: they change at solar terms, not on the first day of a lunar month. If you were born within a few days of early February, the year column is worth a second look. Your birth time matters too, because the change happens at a specific moment, and Saju Birth Time: What the Hour Pillar Needs explains how the calculator treats the time you enter.

Three ways to check the date you have

1. Compare with a document. If any official record exists, enter that solar date and the lunar date separately. Both should give the same four pillars.
2. Check the weekday or the season. A family story like "you were born just after Chuseok" or "on a Sunday" can confirm which solar day a lunar date points to.
3. Ask once, write it down. Note whether the date is solar or lunar, and whether a leap month applies, next to your chart. You will not have to ask again.

Korean and Chinese lunar calendars are calculated for different time zones, and on rare occasions they place the start of a month on different days. If a family record was made with a Korean almanac and the result looks one day off, that difference is a possible reason. An official Korean converter, such as the one published by the Korea Astronomy and Space Science Institute, is a good tie-breaker.

After the date is right

Once your chart is built from the correct day, read it from the reference point outward. How to Find Your Day Master shows which character to start with, and Heavenly Stems and Earthly Branches: A Saju Chart Reference names every character on the chart. If the vocabulary is still new, Saju Meaning: How to Read the Labels on Your Chart covers the basics.

The four-pillar chart is free on PillarAtlas, as described in Free Saju Reading: What You Get Without Paying. Two-person compatibility readings are not available yet, and purchases are not open, so nothing on the site charges a card. Your birth details stay in the page and are cleared when you leave; see the Privacy Policy.

CTA: Enter your solar or lunar date in the Saju calculator

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