Why calculators give different charts

The quickest way in is to see which of the four pillars differs. Each pillar is touched by only a few settings, so knowing which one changed narrows the search to one or two places.

1. Solar term times and the same-minute rule

Your year pillar turns at the Start of Spring and your month pillar at each of the twelve month-opening solar terms (see Solar Term Boundary). Depending on which table a calculator uses and how it handles seconds, the same term can come out a minute apart. We compute the moment astronomically, round the seconds to a minute the way KASI and NAOJ publish, and treat a birth in that same minute as the new term. Our comparison with published tables is in the calculation guide.

2. The Zi hour around midnight

Schools disagree on which day a birth between 23:00 and midnight belongs to. Our default, the single Zi hour, starts the next day's day pillar at 23:00. Choose Late and early Zi in the options and the day pillar stays on the same day, with only the hour stem taken from the next day. Because the day pillar sets your Day Master, this one choice can change much of the reading.

3. Birthplace longitude and the equation of time

Korea Standard Time is set to 135°E, so in Seoul the Sun's position matches a time about 32 minutes earlier than the clock, on average. On top of that comes the equation of time, the seasonal drift of roughly −14 to +16 minutes in when the Sun crosses the meridian. We apply both by default, and you can turn the adjustment off. Against a calculator that doesn't adjust, the hour pillar can differ near the two-hour boundaries, and the day pillar too near the hour the day turns over (23:00 standard time by default, or midnight on a clock set an hour ahead for daylight saving). Against one that adjusts for longitude only, the hour pillar can differ near a boundary, most often for births in February, October and November.

4. Daylight saving and historical standard time

Births in the Korean summers of 1948–1951, 1955–1960 and 1987–1988 were recorded on clocks running an hour ahead. We take that hour back automatically; a calculation that doesn't can land in a different hour, and near the day boundary, on a different day. Korean standard time was also set to 127.5°E in 1908–1911 and 1954–1961, which shrinks Seoul's longitude part to 2 minutes, before the equation of time. Our daylight saving guide works through examples.

5. Luck Pillar rounding and age reckoning

The starting age of your Luck Pillars comes from the days to the nearest solar term, divided by three. We round to a whole number from 1 to 10 and count ages from birth. A calculator using East Asian age reckoning shows the same pillar a year higher, and one that keeps the remainder as months can differ by a few months. More in When your Luck Pillar changes.

6. Lunar birthdays and leap months

A lunar date is converted to a solar date first, so a one-day difference in conversion changes the day pillar. If you were born in a leap month, tick "It was a leap month" on the input screen; otherwise the date is read as the ordinary month with the same number, which falls about a month earlier. We convert on the Korean lunar calendar, checked against KASI data for 1900–2050, or on the Chinese calendar for births in Greater China, Singapore and Malaysia. The two occasionally start a month a day apart, and in 2012 and 2017 even the leap month falls in a different place (see our leap month guide).

7. Unknown birth time

Without a birth time, calculators may settle the year and month pillars and the Luck Pillar starting age from different moments. So if you were born on a solar term day, your month pillar (and your year pillar, at the Start of Spring) can differ from another site's. The moment we use is set out in the unknown-time section of our calculation guide.

In the Detailed view, open "See how this was calculated" below your chart to see the rules applied to your chart, item by item: Zi hour handling, the true solar time adjustment, daylight saving, lunar conversion, a birth on a solar term day and more. You can switch the Zi hour setting and the true solar time adjustment right there; we recalculate and tell you which pillars changed. The reasoning behind your Luck Pillar starting age sits separately, under "How was the starting age set?".

The rules themselves can be revised. When we change one, we raise the calculation basis version; this page describes version 2026-10-19.a. The revision of September 23, 2026, for instance, changed results for births in the exact minute a solar term began and for lunar dates in 1903–1911. Since the revision of October 13, 2026, the true solar time adjustment includes the equation of time. Your hour pillar, and occasionally your day pillar, can differ from what the previous basis gave. Counting every minute of every day once for Seoul births from 1950 to 2025, about 6% of hour pillars and about 0.5% of day pillars changed. That is a count over clock minutes, not over actual births. The changes come from births near a block edge, and by month they were most frequent in November (about 12%) and in February and October (about 11.5%), and under 1.5% in April and June. If the revision changed your result, your calculation notes show the previous basis's pillars for 90 days after it.

1. Use the same calendar (solar or lunar) and the same leap-month setting.
2. Pick the same birthplace city; a different city means a different longitude adjustment.
3. Enter the time on your birth record without removing daylight saving yourself.
4. Match the Zi hour and true solar time settings to the other calculator's.
5. Check whether Luck Pillar ages are counted from birth or the East Asian way.

Any difference left after that may come from the source data itself, such as a solar term time a minute apart. Many of these points have no single settled answer, so we show the rule we chose on every result. Whichever rule a chart follows, its reading is reference information.