About

BirthAlmanac works out what a birth date means — star sign, birthstone, birth flower, weekday, age, generation, Chinese animal and life path number — from real positions and real calendars, rather than from a printed table that rounds.

Why it exists

Star signs are usually printed as a fixed table of dates, and a Chinese animal is easily read off the birth year alone. Both are shortcuts, and both are wrong often enough to matter. Between 1920 and 2026 the sun changed sign on 32 different calendar dates (counted in UTC), and on each of them the sign depends on the year and, in the year of the crossing, on the hour. Every birthday before the lunar new year belongs to the animal before the one the year number suggests. A reference that gets this wrong for a meaningful share of its readers is worse than no reference, because it hands out a confident, incorrect answer.

How the sign dates are worked out

A sign boundary is the instant the sun's ecliptic longitude crosses a multiple of thirty degrees, and that instant drifts by about six hours a year and jumps back at each leap year. So rather than a table of fixed dates, this site uses the instant of every crossing, year by year.

For 1900 to 2100 those instants come from a table computed from VSOP87, the theory of the planets' motion worked out at the Bureau des Longitudes in Paris in the 1980s. It is a long series of terms that says where the earth, and so the sun as seen from it, stood at any moment, and it is the standard theory of its kind: the more exact planetary method in Jean Meeus's Astronomical Algorithms, the standard handbook of the subject, is a shortened form of it. Checked against published times of recent equinoxes and solstices, the table agrees to within a minute. The date pages print each crossing to the minute in UTC, and the calculator turns it into your own time zone and, when the sun changed sign on your birthday, offers a time-of-birth field to settle which side of it you were born on.

The formulae in Meeus's book are still used for the Chinese calendar, below. The calculator answers for years from 1900 to 2100, the span the crossing table covers.

How the Chinese year is worked out

The Chinese zodiac animal is derived from the real lunar calendar, not from the birth year taken modulo twelve. The calendar's own rules are followed: a year runs from new moon to new moon, the eleventh month is the one containing the December solstice, a thirteen-new-moon span gets a leap month, and every instant is measured in Beijing time, as the calendar itself defines it. The new moons, the December solstice and the solar terms are computed with Meeus's formulae, and the new-year dates they give are checked against published ones. Because the lunar new year falls anywhere between 21 January and 20 February, a birthday early in the Gregorian year very often belongs to the animal before the one a simple calculation would give it.

What is reported as tradition, not as fact

Where this site describes what a star sign, a Chinese animal, a life path number or a birthstone traditionally means, it is reporting what a tradition holds, not asserting that it is true or that it predicts anything. The full statement of what this site does and does not claim is on the disclaimer page.

Where the other facts come from

Birthstone and birth flower lists are given from more than one named source where they disagree, rather than presented as a single unattributed consensus: the birthstones as the jewellers' list of 1912 set beside today's, with every change made to it since. Generational ranges carry whoever defined them: the US Census Bureau for the baby boom, the Pew Research Center for the Silent Generation and for Generations X and Z and the Millennials, McCrindle Research for Generations Alpha and Beta, and Tom Brokaw's book of that name for the Greatest Generation. Each notable birth or death is a name, taken from the title of the person's English Wikipedia article, with a birth year, a death year where it applies and a short description from Wikidata (published under a CC0 licence), checked and corrected by hand where needed; any entry is removed on request. See the guides for the detail on each.

Who writes it

BirthAlmanac is published by Inyonitech Solutions (Pty) Ltd. It carries no individual byline and names no author: the site is the work of the organisation, and a calculation is either right or it is not, regardless of who is credited for it.

Corrections

If a calculation, a source or a list here is wrong, write to hello@birthalmanac.com. Corrections are the most useful thing anybody can send.