bazi calculator.

Calendar & supported range

Gregorian birth dates from 1900 through 2100, or valid Chinese lunar dates converting into that range. Lunar leap months must be explicitly selected. Conversion and solar terms use the bundled lunar-javascript 1.7.7 engine. Chinese lunar dates follow its UTC+08 calendar convention; they are not a separate local lunar calendar for every country.

Time, seasons & day boundaries

Enter the recorded local clock time. An IANA time zone resolves its historical UTC offset, including DST, using the browser’s built-in time-zone database. Nonexistent spring-forward times are rejected; repeated autumn hours have a first/second occurrence setting. Longitude is editable, so a city lookup never needs a network request.

True solar time uses the NOAA approximate equation of time: correction in minutes = equation of time + 4 × east longitude − UTC offset in minutes. The corrected local date/time determines the Day and Hour pillars. The Year changes at Li Chun and the Month at the twelve Jie boundaries, compared as physical instants in the engine’s UTC+08 time basis. The default day changes at midnight; the 23:00 alternative is selectable. For midnight mode, the library retains its next-day Zi-hour stem convention after 23:00.

Luck onset & current year

The engine’s minute-based Yun method (sect 2) uses the interval to the preceding or following Jie: three days correspond to one year. Yang-year males and yin-year females run forward; the opposite runs backward. Onset is displayed on the engine’s UTC+08 basis. Ten-year labels and nominal ages follow its calendar-year convention, not exact birthday ages. The current cycle is highlighted by those year labels. The current annual pillar changes at Li Chun, not January 1.

Counts are counts. Strength is a model.

The Five Elements bars count each visible stem and branch once. Hidden stems are shown separately, not silently added to those bars. The disclosed strength model gives a visible stem 1 point (excluding the Day Master), a branch’s element 1, and each hidden stem 0.5; the whole Month pillar is doubled. Support = the Day Master’s element plus its Resource element; support share = support points ÷ total points. At least 55% is labelled stronger, at most 45% weaker, otherwise balanced. These published heuristic thresholds are not a consensus or an accuracy claim. Transformations and special structures can change a practitioner’s assessment.

Unknown time stays unknown

When the hour is unknown, no Hour pillar is invented. Counts and strength use three pillars only. A noon reference is used for displaying the other pillars and provisional luck onset; candidate Year/Month/Day changes are checked at half-hour intervals across the civil day and listed when different. This sampling is not exhaustive at exact term boundaries. Confirm the recorded birth time for boundary-sensitive charts.

Calculation sources & limits

Calendar engine & tests ↗ · NOAA solar-time equations ↗. All calculation code is bundled locally. These links are optional reading; calculating does not contact them. The solar-time equation is an approximation: check boundary-sensitive births against a precise ephemeris. City coordinates represent city centres, not a hospital or exact birth address. The explicit strength formula above is a simplified interpretive model, not an astronomical calculation.