Free tool
Lunar Age Calculator
Your Chinese lunar age, sui, from any birth date, worked out against the real Chinese New Year cutoff rather than the usual “add one year” shortcut.
Dates from 1900-01-31 to 2101-01-28 are supported. Everything runs in your browser.
How lunar age is counted
Traditional East Asian age reckoning differs from the Western count in two ways, and you need both to get the right number:
- You are one at birth. A newborn is counted as being in their first year, so the count starts at one rather than zero.
- Everyone ages together on Chinese New Year. Your lunar age does not go up on your birthday. It goes up on the first day of the lunar year, along with everybody else’s.
Put together, the rule is simply: lunar age = (lunar year now) − (lunar year you were born in) + 1. Note that both years are lunar years. If you were born in January or early February, you very likely belong to the previous lunar year, and that is where most calculators quietly go wrong.
Why “just add one” is not good enough
The shortcut you will see on most sites is to take your ordinary age and add one. That happens to be right for part of the year and wrong for the rest, because it never checks where Chinese New Year falls.
Take someone born on 15 June 1995, working out their lunar age for a conception date in early 2026. Chinese New Year 2026 was on 17 February. On 16 February their lunar age was 31; on 17 February it became 32, four months before their actual birthday. The shortcut reports 31 for both days.
On the gender chart that is not a rounding error. Neighbouring rows differ in a large share of their twelve months, so landing one row out changes the prediction about a third of the time. The calculator above applies the real cutoff, and tells you explicitly when your result is a case the shortcut would get wrong.
Chinese New Year dates
Chinese New Year is set by the moon, falling on the second new moon after the winter solstice. That puts it anywhere between 21 January and 20 February:
| Lunar year | Starts (lunar age rises) | Zodiac |
|---|---|---|
| 2024 | 10 February 2024 | Dragon |
| 2025 | 29 January 2025 | Snake |
| 2026 | 17 February 2026 | Horse |
| 2027 | 6 February 2027 | Goat |
| 2028 | 26 January 2028 | Monkey |
| 2029 | 13 February 2029 | Rooster |
Using lunar age with the gender chart
The Chinese gender chart is indexed by the mother’s lunar age at conception, not her age today, and not her age when the baby is due. To use this tool for that, put your date of birth in the first field and your conception date in the second.
The chart only covers lunar ages 18 to 45. Outside that range there is simply no data, and a calculator that returns an answer anyway is making it up.
Predict boy or girl
Enter two dates and we handle the lunar conversion, the New Year cutoff and leap months for you.
Gender calculator →The lunar calendar explained
New-moon months, leap months, and why lunar month 1 is not January.
How the calendar works →Lunar age questions
What is lunar age?
Lunar age, called sui in Chinese, is the traditional East Asian way of counting age. A newborn is one year old on the day of birth rather than zero, and everyone gains a year together on Chinese New Year instead of on their own birthday. That makes lunar age one or two years higher than the ordinary Gregorian age.
Why is my lunar age sometimes one year higher and sometimes two?
It depends on where your birthday sits relative to Chinese New Year. If your birthday has not yet come round this lunar year, your lunar age is two years above your Gregorian age; once it has passed, the gap narrows to one. Both gaps are normal.
Is lunar age the same as adding one year to my age?
No, and this is the single most common mistake. The “add one” shortcut ignores the Chinese New Year cutoff, so it is only correct for part of the year. On the Chinese gender chart, being one year out changes the prediction in roughly a third of lunar months.
Which lunar age does the Chinese gender chart use?
The chart uses the mother's lunar age at the moment of conception, not her age now or at the birth. Enter your conception date in the second field above to get the right number, then look up that row on the chart.
Does the lunar year start on 1 January?
No. The lunar year begins on Chinese New Year, which is set by the moon and falls between 21 January and 20 February. Someone born in mid-January still belongs to the previous lunar year, which is why January birthdays so often produce a wrong result elsewhere.
Our lunar conversion is tested against an independent reference implementation for every date from 31 January 1900 onward, more than 73,000 days. More about how it is built.