Method
See which rules produce each pillar and how we convert the time recorded at birth.
Year and month boundaries
The year pillar changes at Lìchūn, the Beginning of Spring. The month pillar changes at one of twelve solar terms. These are astronomical instants, so their clock times differ between time zones.
The day and hour pillars
By default, the day pillar changes at 23:00 on the corrected time basis. Choose the midnight convention to keep the civil day pillar until 00:00. The Rat hour spans 23:00–00:59.
From clock time to true solar time
We resolve the recorded local time against the city’s IANA time zone and remove any daylight-saving adjustment. With true solar time on, we add four minutes per degree between the city and the standard meridian, plus the equation of time. The chart shows each correction.
Five Elements and luck cycles
The visible view counts the elements of the displayed stems and branches. The weighted view also includes hidden stems with weights of 1, 0.5 and 0.3. Ten-year cycles follow the year stem and the selected sex for the traditional forward or backward rule. The day-boundary setting also selects the corresponding start-age method.
Unknown birth times
The calculator omits the hour pillar and exact luck-cycle timing when the birth hour is unknown. It flags pillars that may change across a boundary during the birth date.
Engines and test cases
The calculator uses tyme4ts 1.5.6. Development checks use lunar-javascript 1.7.8 to compare pillar output. An independent comparison with sxtwl 2.0.7 covered 4,824 solar terms from 1900 to 2100 and found differences of up to 54.17 seconds. For births close to a solar term, the chart follows the tyme4ts timestamp.