How the twelve intervals work
Each Earthly Branch covers a two-hour interval. Zi (Rat) spans 23:00 through 00:59, Chou (Ox) 01:00 through 02:59, and the sequence continues around the day. Wu (Horse) spans 11:00 through 12:59. At exactly 13:00, the next interval begins. Enter 24-hour time; for example, 1:30 in the afternoon is 13:30.
Midnight belongs to the same branch
23:30 and 00:30 both belong to Zi. That does not settle which day pillar an astrological school uses. Some traditions split early and late Zi or change the day at 23:00; others use midnight. This simple converter identifies the hour branch only, so it does not silently choose a day-pillar rule.
Clock time is not true solar time
The result uses exactly the local clock time you enter. It does not correct for longitude, time-zone offsets, historical daylight saving or the equation of time. Those corrections can move a birth into a different double hour. If your purpose is a BaZi chart, use the life-chart experience with a recorded birth date, time, location and historical time zone.
The branch is only part of an hour pillar
A complete BaZi hour pillar combines a Heavenly Stem and an Earthly Branch. The stem depends on the day stem, so the clock alone cannot determine it. Use this tool to read a traditional time label or understand the twelve-part cycle, not as a substitute for a complete chart.
Sources and calculation method
Hong Kong Observatory conversion tables · 2026 calendar reference · lunar-javascript calculation library
Calculated locally with lunar-javascript 1.7.7. NineHound’s examples and boundary tests are described in our methods; this does not imply independent validation of every date in the supported range.