A four-pillars chart moves the moment of a birth into four pairs of stem and branch: year, month, day and hour. This tool concentrates on getting that conversion right, because the year and the month are not divided by 1 January but by the solar terms, and the hour pillar shifts with the standard time and the longitude of the place you were born. Everything it corrected is printed above the result, so when another chart disagrees with this one you can see exactly where the two parted.
The year pillar starts at the beginning of spring, not on 1 January. That is why people born in January or early February so often turn out to belong to the previous animal year.
The month pillar is divided by the twelve major terms. The minor terms in between — the equinox, for example — do not open a new month.
The day pillar comes straight out of the Julian day number. That 12 August 2026 is a 무오 day is pinned by a test against outside ephemerides.
A four-pillars chart rewrites a moment of birth as four stem-and-branch pairs. Ten heavenly stems and twelve earthly branches mesh into a cycle of sixty, and the year, month, day and hour each take one of them. Eight characters come out, which is why the chart is also called the eight characters.
Each pillar is fixed by a different rule. The year pillar is the sexagenary pair of the year as counted from the start of spring, the month pillar the pair of the month opened by one of the twelve major solar terms, the day pillar a pair that follows directly from the date, and the hour pillar the pair of a two-hour block.
Of these, the year and the month are what people get wrong most often, because the year of the calendar is not the year of the chart and the month of the calendar is not the month of the chart.
In this system the year begins at ipchun, the moment the sun reaches 315° of ecliptic longitude, which falls between 3 and 5 February. That is why births in January and early February so regularly belong to the previous year.
The months are divided by twelve major terms — the starts of spring, of summer, of autumn and of winter among them. Each opens one month of the cycle. The minor terms that sit between them, such as the equinoxes, do not move the month on.
This tool precomputes the times of all twenty-four terms from 1900 to 2100 and ships them as a data file. That keeps astronomical code off the page and stops the same computation being repeated on every visit.
To set the hour pillar correctly you have to know what the clock actually said at the place of birth. Korean standard time began in 1908 on the 127.5° meridian (UTC+8:30), moved to 135° (UTC+9) in 1912, went back to UTC+8:30 in 1954, and has been UTC+9 since August 1961.
There was summer time too: in 1948–1951, 1955–1960 and the summers of 1987–1988 the clock ran an hour ahead. Take a birth time from one of those periods at face value and the whole hour pillar shifts by one block.
Set the place of birth to Korea and this history is applied for you, with a line above the result saying what was applied. For a birth anywhere else the tool asks for the standard-time offset directly.
Standard time is an agreement that lets a wide region share one clock, so it does not match the sun where you actually are. The Korean meridian is 135° east while Seoul sits near 127°, which puts the sun over Seoul about 32 minutes after the clock says noon.
Correcting for longitude alone only does half the job. Because the earth's orbit is elliptical and its axis tilted, apparent solar time runs up to about 16 minutes ahead of or behind mean solar time depending on the season. That difference is the equation of time.
Both are small next to a two-hour hour-pillar block, but for a birth near a boundary the two together move the hour by one place. So each is a separate toggle, and the minutes applied are shown on screen.
The luck cycles are ten-year stretches. Two things have to be settled before the table exists: which direction they run and at what age they start.
Direction follows the polarity of the year stem together with sex. A yang year stem with a male birth, or a yin year stem with a female one, runs forward — onward from the pair after the month pillar. The other two combinations run in reverse.
The starting age is the number of days from the birth to the next solar term when running forward, or to the previous one when running in reverse, divided by three. Since terms are about fifteen days apart, the starting age lands between one and ten.
Converting the eight characters into the five elements — wood, fire, earth, metal, water — shows which quality is abundant and which is missing. This tool counts the four stems and four branches only, not the stems hidden inside the branches; some schools count those too, which is usually why another site gives a different tally.
The ten gods describe how each other stem stands in relation to the day master, the stem of the day pillar, which is to say you. Two axes settle it: the productive and controlling cycles of the elements, and whether the polarity matches. The ten god of the month stem is customarily read as one's place in the world, and the reading starts there.
The void branches are the two branches of the sixty-cycle left without a partner in the ten-day run that the day pillar belongs to. A position holding one of them is read as carrying less weight.
This is a calculator. It builds the chart accurately and joins passages, written in advance by a person, in the order the chart switches them on. Nothing is random, so the same chart always gives the same text — you cannot reload for a different answer.
The reading is not a prediction. It carries over what the tradition has said about each component; the claim that those descriptions foretell anything is not one this tool makes. Do not lean on it for decisions about a career, your health or your money.
Nothing goes to a server and nothing is stored. One static file, the solar-term table, is downloaded, and the rest happens in your browser.
The calculation is the same. Saju (사주) is the Korean name for the four pillars of destiny, BaZi (八字) the Chinese one, and both put the same eight characters in the same four positions. The differences are local: Korean practice corrects for the standard time Korea actually used at the time of birth, keeps its own conventions on the late Zi hour, and names the ten gods and the structures in Korean. Where two traditions genuinely disagree this tool says so rather than picking a side.
Three causes account for nearly all of it. First, whether true solar time is applied — for Seoul that is about 32 minutes, enough to move the hour pillar if you were born near a boundary. Second, the late Zi hour: schools disagree about whether a birth after 23:00 belongs to the next day. Third, births between 1954 and 1961 or during a summer-time period, when the clock in Korea was not what it is now. This tool shows all three on screen and leaves them as toggles.
Because the year begins at ipchun, the start of spring, when the sun reaches 315° of ecliptic longitude — around 4 February. A birth in January 2026 therefore still belongs to the 을사 year of 2025 in this system. It is a rule, not an error.
The other three pillars stand on their own and stay valid. But entering an arbitrary time fills the hour pillar and its ten gods with a wrong value, so if you do not know the time, simply do not read the hour column.
The table for 1900–2100 is precomputed with VSOP87 planetary theory. Checked against 96 equinox and solstice times published by the US Naval Observatory, the largest error was 2 minutes and the mean 0.27 minutes. Every 2-minute case falls in 2100, where ΔT — the slowing of the earth's rotation — is still a prediction. In practice the recorded birth time is the coarser number, which is why a birth within 10 minutes of a boundary raises a warning on screen.
No. One static file — the solar-term table — is downloaded, and every calculation happens inside your browser. The date and time you enter are neither transmitted nor stored.
What this tool bases its numbers on, and how far those numbers go.
Year pillar = the sexagenary pair of the year counted from ipchun (solar longitude 315°). Month pillar = the branch opened by one of the twelve major terms, with the stem derived from the year stem. Day pillar = (JDN + 49) mod 60. Hour pillar = the branch of the two-hour block, with the stem derived from the day stem. Luck cycles = direction from the year-stem polarity together with sex, starting age from the days to the term in that direction divided by three. Times are corrected in the order: the standard time in force then and there, summer time undone, longitude, equation of time.Born 1990-06-15 14:30 in Seoul (126.98° E) → standard time UTC+9, no summer time, longitude −32 min, equation of time about 0 min → the hour branch is taken from 13:58.