Why Do Bazi Calculators Give Different Results?

A Bazi chart is built from your birth date and time, but the calculation depends on conventions that readers and schools do not all share. If your birth data sits well inside a month, day and hour, almost every calculator will agree. The results diverge when the data sits close to a boundary: a solar term, an hour change or midnight.

Below are the main places where calculators differ, and what each choice means.

The Bazi year begins at Lichun (立春), the solar term in early February, usually around 3 to 5 February. It does not begin on 1 January or on Chinese New Year.

So someone born on 2 February 2027 still belongs to the previous year in Bazi, even though the calendar year has changed. A calculator that switches year on 1 January or at Chinese New Year will show a different year pillar for these people, and every other pillar that depends on it may differ too.

See the 2027 Fire Goat year for how Lichun 2027 divides the year.

Bazi months do not follow the calendar months. They begin at the twelve major solar terms (节气, called jie), so each month starts on a particular day and time that changes slightly from year to year.

If you were born within a day or two of a solar term, check that the calculator uses the exact moment of that term, not just the date. A calculator that rounds to the date can put you in the wrong month.

This is the most common source of disagreement. There are three options.

• Standard clock time. The time on your birth certificate, in the time zone of your birth place.
• Local mean time. The clock time adjusted for how far your birth place is from the centre of its time zone, using longitude.
• True solar time. Local mean time plus a small correction for the changing speed of the Earth's orbit during the year.

Some calculators ask for your birth city and correct the time automatically. Others, including ours, use the clock time you enter. Schools differ here. In the school we follow, the chart is built from the local clock time at birth, and true solar time is treated as a reference, for example when a birth time is very close to the boundary between two hours. See the birth-time guide for time zones and daylight saving.

The Zi hour (子时) runs from 23:00 to 01:00. The question is whether a baby born between 23:00 and 23:59 counts as born on the next day or the same day for the day pillar. Schools differ, and calculators follow different rules.

Our free Bazi calculator lets you choose, and when the birth hour is 23 it shows both versions side by side so you can see what changes.

If daylight saving time was in force on the day you were born, the clock time on your certificate is one hour ahead of standard time. Some calculators correct for this automatically using a historical database. Others expect you to adjust it yourself. Time zone rules have also changed over the decades in some places, so for older births it is worth checking.

• Luck Pillars. They run forward or backward depending on gender and the polarity of the birth-year stem, and the start age is worked out from the distance to a solar term. Calculators can round that start age differently.
• Hidden stems and Ten Gods. Which hidden stems are counted, and with what weight, varies between schools.
• Useful God and ratings. Any score or star rating a calculator shows is the author's rule set. Our own are explained on how the star ratings work.

1. Check the time on your birth certificate, and note the birth city.
2. Run the chart on more than one calculator and compare the four pillars, not the interpretation.
3. If the pillars differ, look at which of the cases above you fall into.
4. If your birth time is close to a boundary, ask a reader to check your chart before interpreting it. Master Mandy Lim does this in an online Bazi reading.

A calculator gives you the structure of a chart. It cannot tell you which convention fits your situation, and that is part of what a human reading is for.