How it works

The date and clock time you enter are read at the IANA time zone you pick, using your browser's own time-zone data. A clock time that was skipped when clocks went forward is rejected with a message, because no such moment existed. A clock time that happened twice when clocks went back uses the first occurrence, and the chart says which offset it chose. The chart uses the local clock as entered, with no true solar time correction.

A chart needs a birth hour, because the hour places the life palace and every star is counted from it. With no known time, the calculator says so and stops. It also needs the sex recorded at birth, because the direction of the ten-year periods and of the 長生 stages comes from it, and it offers no default.

The solar date is converted to a lunar month and day in the Chinese calendar. The twelve hour branches each cover two clock hours, with 子 running from 23:00 to 00:59.

Three rules are the calculator's own choice, and the old texts checked do not settle them. The year stem and branch change at the lunar new year, the first day of the first lunar month. A birth from 23:00 to midnight counts as the 子 hour of the next calendar day. In the default chart a birth in a leap month counts as that month through day 15 and as the following month from day 16; with the book setting on, the whole leap month is moved to the next month, the one rule 紫微斗數全書 states.

Starting from the 寅 palace as the first month, the calculator counts forward through the branches to the birth month. From there it counts back through the hour branches, starting from 子, to find the life palace, 命宮. Counting forward by the same number of hours instead gives the body palace, 身宮.

The other eleven palace names then run in order from the 命宮, going against the direction of the branches: 兄弟, 夫妻, 子女, 財帛, 疾厄, 遷移, 僕役, 官祿, 田宅, 福德, 父母.

Each palace gets a heavenly stem from the rule called 五虎遁: the stem of the year fixes the stem at 寅, and the stems then run in order around the palaces from there. The stem and branch of the 命宮 give its 納音 element, one of the five in the sixty-pair cycle, and that element names the bureau: water with the number 2, wood with 3, metal with 4, earth with 5, fire with 6.

The calculator takes the lunar day and adds the smallest number that makes the sum divisible by the bureau number. The quotient counts forward from 寅, starting at 寅 as one. If the number added was even, it moves that many palaces forward from there; if odd, it moves that many palaces back. Where it lands is 紫微.

天府 sits in the palace mirrored across the 寅 and 申 line, so the two share a palace only at 寅 and 申.

Going backward from 紫微: 天機 in the next palace, one palace skipped, then 太陽, 武曲 and 天同 in turn, two palaces skipped, then 廉貞. Going forward from 天府: 太陰, 貪狼, 巨門, 天相, 天梁 and 七殺 in turn, three palaces skipped, then 破軍. Each main star carries a brightness level from a table of seven: 廟, 旺, 得, 利, 平, 不 and 陷. The chart says which table it uses.

The stem of the birth year gives four stars the marks 化祿, 化權, 化科 and 化忌, in that order:

With the book setting on, the 壬 row gives 化科 to 天府 instead of 左輔. For a 庚-year chart, the Conventions assumed section notes that a table on Chinese Wikipedia prints this row of the book differently.

Each palace holds one ten-year period. The first period begins at the age equal to the bureau number, counted the traditional way with a newborn at one, and each later period is ten years on. By default the first period sits on the 命宮 itself. Yang-year men and yin-year women count forward through the palaces; yin-year men and yang-year women count backward. With the book setting on, the first period starts one palace away from the 命宮: on the 父母 palace going forward, or on the 兄弟 palace going backward.

The twelve stages from 長生 to 養 begin at a branch that depends on the bureau: 申 for water and earth, 亥 for wood, 巳 for metal, 寅 for fire. By default they run forward for yang-year men and yin-year women and backward for yin-year men and yang-year women. With the book setting on, they run forward for men and backward for women.

The default chart follows common modern practice as the calculation library this site uses has it. Four rules differ in 紫微斗數全書: 壬 化科 falls on 天府, a leap month moves whole to the next month, the ten-year periods start one palace from the 命宮, and the 長生 stages run forward for men and backward for women. The setting on the calculator switches those four rules together. Every chart lists the conventions it assumed.

The calculator shows placements. It gives no overall verdict on a chart and does not call a chart good or bad.