Last updated: 5 November 2026
Every zodiac site says “we calculate it accurately”. This page shows what we actually compute, where the maths comes from, how far off it can be, and what we do not claim. If you only want your sign, the calculator is that way.
1. There are two boundaries, and they disagree for a few weeks a year
Chinese zodiac years do not start on 1 January. Two conventions are in circulation:
- Lichun (立春) — the solar term that opens spring, falling on 3, 4 or 5 February. Traditional almanacs and most practitioners count the year from this instant, because the solar terms drive the whole system.
- Lunar New Year — the new moon between 21 January and 20 February. Most consumer websites use this, because it is easier to put on a calendar.
Lichun always comes first. The gap between the two is the only period where a birth date produces two different animals:
| Year | Lichun | Lunar New Year | Ambiguous window |
|---|---|---|---|
| 2026 | 4 Feb | 17 Feb | 4–17 Feb |
| 2027 | 4 Feb | 6 Feb | 4–6 Feb |
| 2028 | 4 Feb | 26 Jan | no gap — New Year precedes Lichun |
| 2029 | 3 Feb | 13 Feb | 3–13 Feb |
| 2030 | 4 Feb | 3 Feb | no gap |
Our calculator uses Lichun as the primary boundary. When your date falls inside the window, it shows both results and labels which convention produced each. Outside the window it shows one answer, because there genuinely is one.
2. How the Lichun instant is computed
Lichun is not a date, it is an instant: the moment the sun’s apparent geocentric longitude reaches 315°. We solve for that instant numerically using the low-precision solar theory in Meeus, Astronomical Algorithms (chapter 25), iterating on the longitude until the residual is below a hundredth of a degree, then convert to China Standard Time.
That method is accurate to roughly 0.01° of solar longitude, which is about 15 minutes of time. In practice, against published almanac values for the years we can check:
| Year | Our instant (CST) | Published | Difference |
|---|---|---|---|
| 2020 | 4 Feb 17:07 | 4 Feb 17:03 | +4 min |
| 2021 | 3 Feb 22:57 | 3 Feb 22:58 | −1 min |
| 2022 | 4 Feb 04:45 | 4 Feb 04:50 | −5 min |
| 2023 | 4 Feb 10:33 | 4 Feb 10:42 | −9 min |
| 2024 | 4 Feb 16:21 | 4 Feb 16:27 | −6 min |
| 2025 | 3 Feb 22:08 | 3 Feb 22:10 | −2 min |
| 2026 | 4 Feb 03:55 | 4 Feb 04:02 | −7 min |
So: the date is right, the minute can be off by up to ten. That only matters for someone born within minutes of midnight on 3–5 February. If that is you, tell us your birth time and we will compute your case precisely rather than guess.
3. How the lunar year is computed
Chinese New Year is the second new moon after the winter solstice (or the third, in a year with a leap eleventh month). We convert from the Chinese lunisolar calendar using a standard month-length table and check the result against known dates — 2024-02-10, 2000-02-05, 1987-01-29 all reproduce correctly, as do all 141 years from 1920 to 2060 that we ship.
Both boundaries are generated as data, not typed by hand, and the whole range is published on the years chart. You can check any year yourself.
4. From year to animal, element and polarity
Once the zodiac year is fixed, the rest is arithmetic on the sexagenary cycle:
- Animal = (year − 4) mod 12, in the order Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog, Pig.
- Element = (year − 4) mod 10, mapped to Wood, Wood, Fire, Fire, Earth, Earth, Metal, Metal, Water, Water.
- Polarity = Yang when that stem index is even, Yin when odd.
It is deterministic, and it is why 1924 and 1984 are both Wood Rat years while 2024 is a Wood Dragon. No model, no generation, no drift: the same date always produces the same answer, and you can reproduce it by hand.
5. Where this stops
Four honest limits:
- Time zone. We work in China Standard Time, because the solar terms are defined against it. Someone born in Los Angeles on the boundary day has a local date that can differ from the Chinese one; for those cases the birth time matters, not just the date.
- Birth time. Date-level input cannot resolve a boundary that falls mid-day. We say so rather than pretending otherwise.
- Regional practice. Some schools use the lunar new year boundary, some use Lichun, and a few use the winter solstice. We show the two common ones; we do not claim the others are wrong.
- Reading, not prediction. The calculation is exact. The interpretation on top of it is cultural commentary, and we never present it as a forecast.
6. What we will not do
We do not sell “accurate” as a marketing word while hiding the conventions. We do not tell you a date is unambiguous when two conventions disagree on it. And we do not adjust a result to match what you expected — if the answer surprises you, the boundary is usually why.
7. If we are wrong
Send the page, the date you entered, and what you expected to support@myzodiacguide.com. Date and arithmetic errors get fixed and noted. We will not quietly change a number: corrections are visible.