Your four pillars, on true solar time
A clock does not know where the sun is. This BaZi calculator rebuilds your birth moment from the timezone rule that applied that day, your distance from the zone meridian, and the seasonal drift of the sun — then reads the four pillars from the corrected instant.
BaZi calculator
Your birth city, date, clock time and gender in, four pillars out — with the whole correction shown step by step, plus the ten-year luck pillars that follow.
True solar time
Why the clock is not the sun: longitude, the equation of time and the historical daylight-saving rules.
The hour pillar
The two-hour branches, the midnight day boundary, the late zi hour debate and what moves your hour pillar.
Luck pillars
The ten-year cycle (da yun), the annual pillar and the monthly pillar — which way they run and when the first decade opens.
What is BaZi
Heavenly stems, earthly branches, the day master and the five elements, explained from zero.
Why a birth time needs correcting at all
Your birth certificate records a clock reading. A BaZi chart needs a solar one. The two drift apart for three separate reasons, and they stack:
- The zone you were in. A timezone is a political choice. Its clock is set to a central meridian, and the rules change — China ran summer time from 1986 to 1991, and most of the United States moved its daylight-saving dates in 2007.
- Your distance from that meridian. Every degree east or west is four minutes of solar time. Beijing sits 3.6° west of the 120°E meridian that anchors UTC+08:00, which is about 14 minutes of drift before anything else is counted.
- The equation of time. Even the sun is not a perfect clock. It runs ahead or behind mean time by between about 14 minutes behind and 16 minutes ahead depending on the season.
Add those together and the birth moment can move by more than ninety minutes. Since BaZi changes its hour branch every two hours, that is often the difference between one hour pillar and the next.
What you get
The calculator returns the true solar time in full, the four pillars built from that instant, the day master, and the elements present in the chart. It also shows the wall-clock chart next to the corrected one, so if a pillar moved you can see which one and why.
From there it carries the chart forward in time: the ten-year luck pillars (大运) with the direction they run and the age they start at, the annual pillar (流年) for every year inside each ten-year pillar, and the twelve monthly pillars (流月) under any year you pick.
Everything runs in your browser. There is no account, no upload, and no server storing birth details — the whole calculation is a few kilobytes of JavaScript.
How to use it
- Type your birth city and choose it from the list, so the tool gets both longitude and timezone rule.
- Enter the date and the clock time exactly as they were recorded, including any daylight saving.
- Choose male or female — that sets which way the ten-year luck pillars run.
- Read the true solar time, then the four pillars beneath it — and check the correction chain if you want to see the working.
Two schools disagree about births between 23:00 and midnight. If that applies to you, the hour pillar page explains the choice, and both settings are available in the calculator.
Frequently asked questions
What is a BaZi calculator?
A BaZi calculator turns a birth date and time into the four pillars: a year, month, day and hour pair drawn from the heavenly stems and earthly branches. Those eight characters are the raw material of a BaZi reading. The hard part is not the arithmetic, it is working out which instant to calculate from.
Why is my hour pillar different here?
Because this calculator converts your birth clock to true solar time first. Longitude, historical daylight saving and the equation of time can together move your birth moment by more than an hour, which is enough to cross a two-hour branch boundary and change the hour pillar entirely.
What is the difference between BaZi and the Chinese zodiac?
The zodiac animal is just the earthly branch of the year pillar, one character out of eight. A full BaZi chart also uses the month, day and hour, which is why two people born in the same zodiac year can have very different charts.
Does the calculator handle birth outside China?
Yes. The timezone engine covers the world, including the historical daylight-saving rules of each country, so a birth in New York, London, Sydney or Sao Paulo is corrected with the rules that actually applied there on that date.
Is this free?
Yes, the chart is free and there is no sign-up. It runs entirely in your browser, so your birth details are never sent to a server.