Calculation notes
Methodology
This page describes the rules currently used by this calculator. It makes the calculation reproducible within the site’s stated conventions; it does not treat a traditional interpretation as a scientific prediction.
Inputs and civil time
The calculator uses the recorded Gregorian birth date and local clock time, selected birth location, sex selection used by the traditional cycle rule, and selected reading year. The selected location supplies a reference longitude and an IANA time-zone identifier. The runtime derives the historical UTC offset for the entered date, including daylight-saving changes where they apply. If the birth time is unknown, the calculator labels the result as estimated rather than treating noon as a documented birth time.
Solar-time adjustment
Before deriving the pillars, the calculator adjusts the entered local time using the difference between the location’s reference longitude and the time-zone meridian, plus an equation-of-time estimate for that date. The historical daylight-saving difference is removed from that adjustment. This is the site’s declared solar-time convention, not a claim that every BaZi school uses the same convention. A result near midnight or a traditional two-hour boundary can change when the adjustment crosses that boundary.
Calendar and chart calculation
The adjusted date and time are passed to the lunar-typescript calendrical library to derive the Year, Month, Day, and Hour Pillars. The Day Master is the stem of the Day Pillar. Ten Gods are calculated by comparing a stem’s Five Element and yin/yang relationship with the Day Master. The annual pillar is taken from a mid-year reference date in the selected year so that the displayed annual label is not affected by a New-Year boundary lookup.
Element display and ten-year cycles
The Five Elements display is a rule-weighted comparison, not a count of characters or a percentage of fate. It combines visible stems, hidden stems, and month-branch context. Ten-year-cycle direction and start timing are generated by the calendrical library using the selected sex and the traditional year-stem rule. These outputs are traditional calculation categories, not measured traits, probabilities, or professional advice.
Why results can differ
Another calculator may use a different place reference point, historical time-zone data, day boundary, solar-time method, solar-term convention, hidden-stem display, or ten-year-cycle rule. Compare the birth record and calculation settings before comparing interpretations. Use the calculator comparison checklist for a step-by-step audit and the sources page for the site’s external references. Last reviewed: September 1, 2026.