How the chart works
The Chinese gender chart, also called the Chinese birth calendar, is a grid. Down the side is the lunar age of the person who is pregnant at the time of conception, from 18 to 45. Across the top are the twelve months of the Chinese lunar calendar. Each square says boy or girl. To read it, you need two numbers: your lunar age at conception and the lunar month in which the baby was conceived.
Many websites skip the lunar part and use your usual age and the calendar month. That gives a different square, and often a different answer. This calculator does the conversion properly, with the Chinese calendar data published by the Hong Kong Observatory.
Lunar age and lunar months
Lunar age is the traditional way of counting age in China and other parts of East Asia. A baby is 1 on the day they are born, and everyone gains a year at Chinese New Year, not on their birthday. So your lunar age is the number of Chinese New Years you have lived through, plus one. It is usually one or two years more than your age in years.
Lunar months start on the day of a new moon and last 29 or 30 days. Twelve of them make about 354 days, so the calendar adds a thirteenth month, a leap month, about seven times every 19 years to stay in step with the seasons. Chinese New Year therefore moves around and always falls between 21 January and 20 February. A leap month repeats the number of the month before it, and the calculator reads it as that month, as most versions of the chart do.
A worked example
Say you were born on 1 January 1995 and the baby was conceived on 15 June 2024.
- Chinese New Year 1995 fell on 31 January, so on 1 January 1995 it was still lunar year 1994. You were born in lunar year 1994.
- Lunar year 2024 began on 10 February 2024, so 15 June 2024 belongs to lunar year 2024.
- Your lunar age at conception is 2024 minus 1994, plus 1: 31. In usual years you were 29.
- On the lunar calendar, 15 June 2024 is the 10th day of the 5th month.
On the chart, lunar age 31 and month 5 give girl. Read with your usual age and the Gregorian month instead (29 and June), the same chart would have said boy.
Where the chart comes from
The story usually told is that the chart was found in a royal tomb near Beijing about 700 years ago and kept secret at the imperial court. No historical source for this story has ever been shown, and the versions circulating today differ in a few squares. The one used here is the version most often published.
Does it work?
No more than chance. Researchers in Sweden and the United States tested the chart on 2.8 million births recorded in Sweden between 1973 and 2006, using the mother's lunar age and month of conception. It was right for 50% of babies, exactly what you would expect from tossing a coin.
There is a simple reason. A baby's sex is decided at fertilisation, by whether the sperm carries an X or a Y chromosome. That is close to an even chance every time: about 105 boys are born for every 100 girls, around 51% boys. Neither the mother's age nor the month changes it in a way the chart could predict.
So enjoy the chart the way you would enjoy a horoscope or the ring-on-a-string test: as something to laugh about together, or a little bet with friends and family, and not as a reason to paint the nursery.
Finding out for real
If you want to know before the birth, the anomaly scan, usually between 18 and 22 weeks, can often show the sex if the baby is lying in a good position and you ask to be told. In many countries a blood test called NIPT, mainly used to screen for chromosomal conditions, can also show the sex chromosomes from about 10 weeks. Your midwife or doctor can tell you what is offered where you live.