How We Calculate
This page explains how the calculations on the site work: where the formulas come from, which variants we choose where traditions diverge, and what is known about tests of the methods described.
Principles
The calculation is open. Every calculator page describes the formula, and the result can be reproduced by hand. If you need an example to check it, it is right there.
The variant is chosen explicitly. In almost every method, schools disagree. We choose one variant and say which one it is and how it differs from the others.
No rigging. Random methods use the browser's random number generator with fair probabilities. We do not skew results toward pleasant answers, and we show the real probabilities wherever they can be calculated: dice sums, hexagram odds, the share of doubles in dominoes.
Specific choices
| Method | What we chose |
|---|---|
| Life Path Number | day, month and year reduced separately; master numbers 11, 22, 33 are not reduced |
| Chinese year | the boundary is Lichun, the moment the Sun passes 315° of the ecliptic (February 3–5), not January 1 and not the Lunar New Year |
| Lunar calendar | true positions of the Moon and the Sun (the main terms of Meeus's lunar theory); new and full moon times accurate to within 5 minutes, dates in Moscow time; lunar days counted in 24-hour steps from the new moon, with the number given for noon Moscow time |
| Mayan Tzolkin | GMT correlation 584283 |
| Flying Stars | flight order across the Lo Shu grid; the polarity of star 5 is taken from its palace; the annual and monthly stars change at Lichun and at the jie solar terms |
| Kua Number | for men, the year star on the Lo Shu grid; for women, the number that complements it to 15; a 5 becomes 2 for men and 8 for women |
| BaZi and Saju | solar term times from the VSOP87 theory, with tables for 1900–2100 accurate to the minute; true solar time is a longitude correction plus the equation of time; by default the day changes at 23:00; the year and month follow the jie solar terms or, optionally, the lunar calendar; the starting age of the Luck Pillars is rounded to whole years |
| Chinese Calendar | a month begins on the day of the new moon in Beijing time; the leap month is the first month without a principal term (zhongqi) in a thirteen-month year |
| I Ching | three-coin method with probabilities 1/8, 3/8, 3/8, 1/8, not yarrow stalks |
| Tarot and runes | random draw from the full deck or rune set, with no repeats within a spread |
| Zodiac sign compatibility | a scale based on the angle between signs; it is our own, and we say so |
What is known about tests
A brief summary of the methods that have been tested.
Astrology. Shawn Carlson's experiment, published in Nature in 1985: astrologers could not match birth charts to psychological profiles better than chance. Later studies and meta-analyses give the same result.
Biorhythms. The 23/28/33 theory has been tested many times since the 1970s; reviews of dozens of studies found no link to performance or accident rates.
Zodiac sign compatibility. Studies comparing birth dates in marriages and divorces across large samples found no systematic link.
Random methods. Cards, dice, coins and the coin version of the I Ching are random number generators. We calculate and show their probabilities; a random result has, by definition, no predictive power.
For most of the other methods, no tests have been conducted at all, and their pages say that too.
Why we do it anyway
Because divination systems are a large part of human culture, they are built in interesting ways, and they deserve to be understood properly rather than through retellings.
And because they have a side that works and needs no mysticism: a random sign or a calculation sets a frame in which a person puts into words what they already knew about their situation. That, not prediction, is what happens when a reading “comes true.”
That is why we try to make the calculation accurate, the description honest, and to make no promises at all.