BaZi calculator
Free, no sign-up, and it shows its working. Enter a birth time and you get the four pillars plus every correction applied to get there — so you can check it against any other source.
What this calculator does that most don’t
Each of these is demonstrated by a permanent test case in the verification corpus — follow the link on any point to see the worked case.
Historical time zones, not current ones
Singapore ran UTC+7:30 until 1982. Hong Kong observed summer time until 1979. Mainland China ran nationwide daylight saving from 1986 to 1991 — a cohort most calculators silently miscast, because they apply today’s offset to a 1980s birth. See the case →
The equation of time, not just longitude
Longitude alone gives Local Mean Time — a fictional, even-paced sun. The real sun runs up to ~16 minutes ahead or ~14 minutes behind it. Near a two-hour boundary, that difference decides the hour branch. Most calculators apply no equation of time at all. See the case →
True solar time is not fed into the year pillar
A solar term is one worldwide astronomical instant. A chain that corrects the clock to true solar time and then compares that reading against the term table gets the YEAR pillar wrong for births near Li Chun — the New York case below shows a whole-year error. See the case →
Daylight-saving edge times are flagged, not guessed
A birth time inside the spring-forward gap never occurred; inside the fall-back overlap it occurred twice. Both are detected here and warned about, rather than silently resolved to whichever instant the library prefers. See the case →
If your chart differs from another site
The most common reasons are shown directly in the trail above: the other site read the hour off clock time rather than true solar time; it takes the opposing late-zi day boundary; it uses civil midnight rather than true solar time for the day boundary at all; or it compared a solar-corrected reading against the solar-term table, which shifts the year pillar near Li Chun. These are set out in the conventions, and the verification corpus shows several as worked cases — though not every possible source of disagreement is listed here.
Related
What the four pillars are · Finding your Day Master · The 2027 forecast