Why your chart looks different on another site

The six settings to compare first

A four-pillar chart is calendar arithmetic, and every calculator, Korean saju, Chinese BaZi or Japanese 四柱推命, runs the same sixty-cycle. What they don’t share is a handful of conventions around the edges of a year, a day and an hour. Most birthdays sit nowhere near those edges, which is why most people get the same chart everywhere. If yours differs, one of these is usually the reason.

Start with the lunar-birthday question, because a lunar date entered as a solar one changes the whole chart. The other settings only matter if you were born near the edge of a year, a month, a day or a two-hour block.

Six example births, calculated both ways

Here each convention is switched on its own, with everything else held fixed. The people are invented; the pillars are not. They come from the same engine as our free chart, and if the engine ever stopped producing a difference, this page would fail to build rather than show you a stale example.

Ipchun or Lunar New Year: where the year begins

In saju the year turns at Ipchun (입춘, 立春), the start of spring, not on January 1 and not on Lunar New Year. The Encyclopedia of Korean Culture puts it plainly: in the divination arts the new year begins at Ipchun, and each month begins at the start of its solar term, not on the 1st (사주, E0025957). BaZi uses the same rule. Many zodiac charts online, though, switch animals at Lunar New Year, which from 1930 to 2031 falls anywhere from 14 days before Ipchun to 16 days after it.

So a baby born on February 10, 2026, is 丙午, a Horse, in any calculator that follows the saju and BaZi rule, because Ipchun came at 5:02 AM on February 4 in Seoul. A site that counts from Lunar New Year, which fell on February 17, 2026, still calls the same baby a Snake. Ipchun is also a single instant, not a date: that same moment was 3:02 PM on February 3 in New York, the afternoon before. Born on Ipchun day itself, you need the time (Ipchun, year by year).

A lunar birthday typed into a solar calendar

Some families record birthdays by the lunar calendar (음력, eumnyeok), and a lunar date typed into a solar date box produces a completely different chart. Take a fictional birth on Chuseok, the 15th day of the 8th lunar month, in 1995. That day was September 9, 1995, and its day pillar is 癸卯. Typed in as “August 15, 1995,” the chart gets day 戊寅, a different Day Master, and here a different month as well, 甲申 instead of 乙酉.

Our forms take solar (Gregorian) dates only, so convert first. For a Korean lunar date, use the converter of the Korea Astronomy and Space Science Institute (KASI converter); for this example it returns the same solar date, with the day written 계묘 (癸卯). Korean and Chinese lunar calendars start each month on the day of the new moon in their own time zone, so in rare months they are a day apart, as they are at the start of 2027 (Korean vs Chinese zodiac).

Time zone and daylight saving

A birth time only means something with the clock it was read on. Our engine turns your local time into an exact moment through the IANA time zone database for your birthplace, which records each place’s standard time and daylight saving history (IANA). Calculators that assume one fixed offset, or that ask you to type a UTC offset, slip whenever summer time applied.

The example in the table is a New York birth at 7:21 PM on August 7, 1995. Clocks were on summer time (UTC-04:00), and the solar term that opens the next month, Start of Autumn (立秋), came about half an hour later, so the month pillar is 癸未. Read the same clock as standard time and the birth moves an hour later, past the term: month 甲申. The year and day don’t change; the month, and every ten god it carries, does.

Korean births need one more check, because Korea’s clocks have moved (what’s distinctly Korean about saju has the meridian history). What a calculator needs is the offset on your birth date: Korean clocks ran on UTC+8:30 from 1954 to 1961, and summer time put them an hour ahead in 1948–1951, 1955–1960 and 1987–1988 (시법, E0032366). The IANA data holds the same history, so a calculator that asks for your birthplace picks it up, while one that assumes UTC+9 for every Korean birth is half an hour or an hour out on those dates. Use your birthplace, not where you live now.

Midnight or 11 p.m.: when the day turns

The two-hour block of the Rat, 子, runs from 23:00 to 01:00, straddling midnight. Some calculators start the new day with that block, at 23:00; others, like our chart form, start it at midnight. The Encyclopedia of Korean Culture records the split: some readers divide the Rat hour into a “night Zi” (야자시, 23:00 to midnight) and a “proper Zi” (정자시, midnight to 01:00) and set the day pillar accordingly (사주, E0025957). A developer write-up on calculator mismatches lists this day boundary as one of three unsettled conventions, with the year boundary and the hour clock, and notes that it only touches births between 23:00 and 23:59 (RoxyAPI).

For those births it touches the most important character in the chart. Our fictional Seoul birth at 11:30 PM on May 18, 1996 has day 乙卯 under the midnight rule and 丙辰 under the 23:00 rule: Day Master 乙 Yi (yin wood) or 丙 Bing (yang fire). The hour pillar is 戊子 either way, because under our split (“late Zi”) convention the 23:00 hour already takes the next day’s stem. Our chart flags these births; if you were born in that hour, read both Day Masters and see which one you recognize.

Clock time or solar time, and Korea’s half hour

Clocks follow a time zone’s meridian; the sun follows your longitude, at four minutes of time per degree. Korea keeps Japan’s meridian, 135°E, so in Seoul, at 126.98°E, the sun reaches its average noon about 32 minutes after the clock does; the encyclopedia’s entry on time-keeping gives the same 32-minute gap for Seoul (시법, E0032366). Korean practice handles that gap in two ways. A practitioner guide takes 127°30′E as the longitude that fits Korea, half an hour behind the clock, and shifts every two-hour block by 30 minutes, so the Rat hour runs from 11:30 p.m. to 1:30 a.m. (정해 만세력, lecture 08). The encyclopedia records readers who fix the Seoul day change to the second, at 0:32:47 a.m. (사주, E0025957). Calculators that offer “true solar time” add one more term, the equation of time: over a year the sun runs up to about 14 minutes behind and 16 minutes ahead of an even clock (NOAA).

Our engine can do this, but our chart form uses clock time. With solar time switched on for Seoul, the fictional 12:20 AM birth becomes 11:51 PM the evening before, and the day pillar falls back from 乙卯 to 甲寅. The 1:10 AM birth stays on the same day but moves from the Ox hour (丁丑) to the Rat hour (丙子). Neither choice is wrong. If a Korean app shows you a different hour pillar, a half-hour shift is the first thing to check.

Hidden-stem and twelve-stage tables

Sometimes the eight characters match and the reading still differs. Each branch carries hidden stems, and schools list them differently: our three-stem 人元 table holds only 癸 inside 子, while five of the six school tables in one Japanese comparison add 壬 (six tables compared). For a 丙 Bing (yang fire) Day Master, that branch is a Direct Officer in our table and a Direct Officer plus a Seven Killings in the tables that add 壬; two of them (三命通会 and 玉井奥訣) also list 辛, a Direct Wealth. Same pillars, one or two extra ten gods (hidden stems explained).

The twelve stages vary the same way. We run yin stems backward from their starting branch, and let 戊 follow 丙 and 己 follow 丁 (火土同根, “fire and earth share a root”). Japanese Wikipedia’s entry on the stages describes both disputes: many readers give a yin stem the same stages as its yang twin, and earth is placed either with fire or with water (水土長生) (十二運). A site that prints a different stage name for your Day Master may simply be using the other table (our settings).

Can ChatGPT read my saju?

A language model predicts text, and a chart is not text. Unless the chatbot passes your birth data to real calendar code, the pillars it gives you are its best guess at what a chart should look like, and the six settings above are exactly where a guess slips: the minute of a solar term, a lunar conversion, the summer-time rule of a birthplace in 1995. If the day pillar is off, so is the Day Master, and the long, confident reading that follows describes a chart that isn’t yours.

A quick test: ask it for the exact minute of Ipchun 2027 in Japan time and compare with the National Astronomical Observatory of Japan’s almanac, which lists 10:46 on February 4, the same minute our engine computes (NAOJ 2027 almanac). Better still, calculate the chart first and give the chatbot the finished pillars. That is how this site works: code computes every chart, and our paid reading is then written by AI (Claude) in Horan’s voice from those computed facts, and we say so plainly (how we calculate).

Is saju accurate?

Two different questions hide in that one. The first is about arithmetic: given a birth moment and a set of rules, is the chart right? That one has an answer you can check yourself, with the six settings above and an almanac such as NAOJ’s or KASI’s. The second is about life: does the chart foretell what happens to you? Nobody has shown that it does, and we don’t sell it as a forecast. Ten calculators that agree prove only that ten programs share their rules.

So this page can promise you a checkable chart, and nothing about your future. What the tradition adds on top of the arithmetic is a vocabulary, images and tendencies attached to each character that schools read differently. Treat a reading as a prompt for thinking about your own habits, not as grounds for a decision about health, money, law or relationships (what a reading can and can’t do).

No birth time? What still holds

Without a time you still get three pillars, year, month and day, and so the Day Master. They hold unless your birthday sits on a boundary. On a day when a solar term changes the month (or, around February 4, the year), the minute decides, and our free chart leaves that pillar blank rather than guessing. If you might have been born between 23:00 and midnight, the day rule decides, and a date-only chart uses the date as given, which is the midnight rule.

What you lose for certain is the hour pillar, two of the eight characters. A calculator that fills it in without a time is guessing, and a claim that a date alone captures some fixed share of your chart is a number nobody has measured.

Our settings, in one place

Our chart form counts the year from the Ipchun instant, the months from the twelve jie terms, uses your birthplace’s IANA time zone with its daylight saving history, turns the day at midnight, keeps clock time, and uses the three-stem hidden-stem table. The engine also supports the 23:00 day boundary and solar time. The full list, with the tests we run, is on the how we calculate page, and the free saju calculator explains what each field does.

About this page

Written with AI (Claude) from the sources listed and our calculation engine. Horan and Kachi are fictional characters, and nothing here predicts events. The rules behind every chart: how we calculate.