I celebrate my lunar birthday on a different solar date every year. Which year does Saju use?

Only one date: the lunar date of the year you were born, converted to that year's solar date. The solar birthday that shifts every year has nothing to do with Saju.

If my lunar birthday is in early January, does my zodiac animal change?

The zodiac animal (Year Pillar) in Saju is based on Ipchun, not Lunar New Year. Even in early lunar January, if it is before Ipchun, you are read as the previous year's animal.

Calculation Standards

I only know my lunar birthday. Can I still get a Saju reading? What about leap months?

As of 2026-10-24 · Edited by Sajunyang · about 1900 characters

One-line answer

Yes. Saju is based on solar terms rather than the lunar calendar, so a lunar birthday is first converted to the solar date and then the chart is built. The Korean lunar calendar, based on the Korea Astronomy and Space Science Institute, differs from the Chinese lunar calendar in some years, so it must be converted with Korean data, and a leap-month birth must always be marked as such. The same 'lunar April 15' falls a full month apart in the solar calendar depending on whether it is the regular month or the leap month.

Isn't Saju read by the lunar calendar?

A common misconception. The Year Pillar changes not on lunar January 1 (Lunar New Year) but at Ipchun, and the Month Pillar changes not with the lunar months but at the solar terms. The solar terms are determined by the sun's position, a system much closer to a 'solar calendar'. So a lunar birthday is only an input for building the chart, and the calculation is done with the solar date and time. Saju was read by the lunar calendar in the old days because the calendar of the time was lunar (strictly, lunisolar).

Why does the leap month matter?

Twelve lunar months come to 354 days, drifting 11 days from the solar year, and to make up the gap a leap month is inserted 7 times in 19 years. In a year with a leap month, a month of the same name occurs twice; in 1990, for example, there was a regular 5th month and a leap 5th month. Enter a leap-5th-month 15th birth as a regular 5th month 15th, and the solar date lands a month earlier, changing the whole Month Pillar. If your official birth registration marks the lunar birthday as a leap month, you must check that box.

The Korean and Chinese lunar calendars use different reference meridians (135°E for Korea, 120°E for China), so when the new moon falls near midnight the start of the month shifts by a day, and in rare cases even the position of the leap month differs. Births in Korea must use the Korea Astronomy and Space Science Institute's lunar calendar. Sajunyang converts the years 1910–2049 using korean-lunar-calendar data.

FAQ

I celebrate my lunar birthday on a different solar date every year. Which year does Saju use?: Only one date: the lunar date of the year you were born, converted to that year's solar date. The solar birthday that shifts every year has nothing to do with Saju.
If my lunar birthday is in early January, does my zodiac animal change?: The zodiac animal (Year Pillar) in Saju is based on Ipchun, not Lunar New Year. Even in early lunar January, if it is before Ipchun, you are read as the previous year's animal.

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This article is reference material summarizing traditional Saju theory and does not replace medical, legal or investment judgment. Our calculation standards are published at About Sajunyang.