What a bazi calculator can tell you from a birthday alone
A bazi chart is built from four pillars: year, month, day, and hour. Most calculators ask for all four. But three of them only need your birthday — and the fourth needs information most people don't have.
The four pillars, and what each one actually needs
| Pillar | What it needs | From a birthday? |
|---|---|---|
| Year | The year, split at the start of spring | Yes |
| Month | The month, split at solar terms | Yes |
| Day | The day itself | Yes |
| Hour | The hour you were born | No |
Two things that surprise people
The year doesn't change on January 1
In bazi, the year turns at the start of spring — around 4 February in the Gregorian calendar, not 1 January and not Chinese New Year. Someone born in late January belongs to the previous year's pillar.
The month doesn't change on the 1st either
Months are set by solar terms, which land around the 4th to the 8th of each Gregorian month. Because the boundaries are astronomical rather than fixed, the twelve months run anywhere from 29 to 32 days. A calendar-month calculator will get this wrong; a solar-term calculator won't.
The day pillar is different again: it simply runs a fixed 60-day cycle, with no reference to months or years at all.
What the missing hour costs you
The hour pillar carries the finer detail — it's traditionally tied to later life and to the inner layer of a chart. Without it you can still work with the three you have, and in practice the day master and the month are where most readings start anyway.
What you can't honestly do without the hour is present a complete four-pillar reading. Any calculator that offers one from a birthday alone is filling in the gap with something that isn't there.
What this calculator does
- Computes the year, month, and day pillars from your birthday, using solar terms.
- Finds your day master — the stem of your day pillar.
- Gives you a short reading for today, built from your day master and your birth month against the current day's pillar.
- Runs entirely in your browser. Your birthday is never uploaded.
It does not do a full four-pillar reading, and it doesn't pretend to. That needs your birth hour.
See it with your own birthday
Two fields, no sign-up, nothing uploaded. You'll get a card you can keep or send.
Open the calculatorQuestions people ask
- Why do I need to give a birthday at all — can't it just be random?
- It could be, but then it would be a different thing. This reading is fixed by your birthday and today's date, so the same inputs always give the same card. Nothing is generated on the fly.
- Do you store my birthday?
- No. The calculation happens inside the page. If you come back tomorrow, your browser remembers the birthday locally so you don't retype it — that's your device, not ours.
- Is a bazi calculator the same as a Chinese zodiac calculator?
- No. A zodiac calculator reads one pillar (the year). Bazi uses all four. They disagree routinely — most famously for people born in the first weeks of a year.