The start of spring is not always 4 February
Published 2026-08-20
The start of spring (立春, lichun) is the boundary Eight Mansions (八宅, Ba Zhai) counts your birth year from, and it is not a fixed date. It is an astronomical moment, and across 1900–2100 it lands on 3 February in 39 years, on 4 February in 128 years, and on 5 February in 34 years.
So a calculator that hardcodes 4 February is working from the wrong boundary in 73 of those 201 years. For a birthday in the middle of February that costs nothing. For a birthday in the first days of February it can put you in the wrong year, which gives a different Kua number and a different set of four directions.
The distribution, counted from this site’s calendar table
| Date spring begins | Years, 1900–2100 |
|---|---|
| 3 February | 39 |
| 4 February | 128 |
| 5 February | 34 |
The three dates are not scattered evenly through the range, and that turns out to matter more than the raw counts. Every 5 February in the table is 1980 or earlier — the last one is 1980. Every 3 February is 2017 or later — the first one is 2017. Between 1981 and 2016 there is no exception at all: the boundary is 4 February in all 36 of those years.
That is why the hardcoded date survives. Anyone born between 1981 and 2016 gets the right answer from a calculator that never looks the date up. Push either side of that window and the shortcut starts failing: births up to 1980 are the ones a hardcoded 4 February pulls a year too late, and births from 2017 on are the ones it pulls a year too early.
A birth date where it changes the answer
Take 4 February 1980. The start of spring that year was 5 February 1980 at 00:09 (UTC+8), so 4 February still belongs to the 1979 solar year — at any hour of the day, which makes this a clean case with no birth-time ambiguity in it.
Run that date for a man and the site returns Kua 3, the trigram Zhen, East group. A calculator that assumes the boundary is 4 February counts the same birth as 1980 and returns Kua 2, Kun, West group. Those are not adjacent answers. Here are both charts side by side:
| Direction | Kua 3, East group | Kua 2, West group |
|---|---|---|
| North | Tian Yi, favored | Jue Ming, weak |
| Northeast | Liu Sha, weak | Sheng Chi, favored |
| East | Fu Wei, favored | Huo Hai, weak |
| Southeast | Yan Nian, favored | Wu Gui, weak |
| South | Sheng Chi, favored | Liu Sha, weak |
| Southwest | Huo Hai, weak | Fu Wei, favored |
| West | Jue Ming, weak | Tian Yi, favored |
| Northwest | Wu Gui, weak | Yan Nian, favored |
The four directions one chart treats as favored are the exact four the other treats as weak, and nothing in the output of either calculator tells you which one you are holding.
Sometimes the same error is harmless
The same birth date, run for a woman, goes differently. Correctly counted as 1979 it returns Kua 3; counted as 1980 it returns Kua 4. Both are East group, and both have the same four favored directions — north, east, southeast and south. What changes is which star name sits on each of them: the four labels rotate, so the direction called Sheng Chi in one chart is called Yan Nian in the other.
Whether the boundary error flips your whole chart or only relabels it depends on which two years you are between. That is a reason to get the date right, not a reason to assume the worst.
Born on the boundary day, the hour is the answer
When your birthday is the boundary day, the date is not enough. The start of spring in 2025 was 3 February 2025 at 22:10 (UTC+8). A man born at 21:00 that evening belongs to the 2024 solar year and comes out Kua 3, East group. Born at 23:00 the same evening, he belongs to 2025 and comes out Kua 2, West group. Under two hours apart, opposite groups.
This is why the Kua number calculator asks for a birth time only when the birthday lands on the boundary day for that particular year. On any other date the hour makes no difference, and asking for it would only invite a guess. If your birthday is 3, 4 or 5 February and you do not know the hour, the honest position is that you have two candidate Kua numbers, and you should run both rather than pick the one you prefer.
What the boundary does not tell you
One limit is the zodiac. The animal does not turn at the start of spring — it turns at Chinese New Year, which is a different date, and in some years the two are more than two weeks apart. Neither boundary is a correction of the other; they answer different questions, and which one applies when is a separate article.
The other is scope. Getting the boundary right tells you which year to count from and therefore which of the eight directions Eight Mansions names as favored for you. It does not say that facing one of them does anything measurable, and we do not either. The times are computed for UTC+8, so a birth in another time zone close to the boundary hour needs converting first, and the calculator does not do that for you. The table covers 1900–2100; outside that range this site has no answer rather than a guessed one. See method and assumptions for the rest of what we compute and where we stop.