What Your Birth Hour Means in BaZi

Chinese timekeeping does not use twenty-four equal hours for this purpose. It uses twelve 时辰 — two-hour blocks, one per earthly branch, and therefore one per animal.

Your birth hour determines the last of the four pillars. Year, month and day you can get from any calendar; the hour you can only get from a birth time, which is why it is the pillar most often missing.

The twelve periods

Note that the first one straddles midnight. The rat hour runs from 23:00 to 01:00, so someone born just after 11 pm belongs to the next day's rat hour — a detail that changes the day pillar at the other end of the chart.

What the hour changes

The hour pillar is a stem plus a branch. The branch comes from the clock; the stem is derived from the day's stem by a fixed rule, so the hour cannot be guessed independently.

In practice the hour refines the reading in the personal direction: the year describes circumstance, the month the season, the day you — and the hour what you are pointed at. Two people with identical dates but different hours can read quite differently.

It also settles the edge cases. A birth at 00:55 and one at 01:05 land in different branches, and the first one belongs to the previous calendar day for chart purposes.

If you do not know your birth time

Leave it out. A three-pillar chart is honest; a four-pillar chart with an invented hour is not, and the invented part sits exactly where the most personal reading should be.

The practical situation on this site: the birth chart tool accepts a date alone and marks the chart as three pillars. If you later find the time on a birth certificate, add it and the fourth pillar appears.

Hospital records, family memory and old identity documents are the usual places to look. If the time is remembered as 'around dawn' or 'before lunch', that is often enough to place the branch.