Chinese gender predictor: the chart, your lunar age and the evidence

How the Chinese gender chart works

The Chinese gender chart, also called the Chinese gender calendar or the Chinese birth chart, is a grid of 28 rows and 12 columns. Each row is the mother's lunar age at conception, from 18 to 45, and each column is the lunar month of conception. Each cell says boy or girl. A Chinese gender calculator such as this one works out the row and column from ordinary dates and reads the cell. The full chart is shown above.

Lunar age is not your age plus one

The chart counts age in the traditional Chinese way, called xusui. A person is 1 at birth and becomes a year older at each Chinese New Year, not on their birthday. Lunar age is therefore one or two years more than age in completed years, depending on where the birthday and the conception date fall relative to New Year. Adding one to your age gives the wrong row about half the time.

A worked example: a mother born on 26 January 1990 has a due date of 15 January 2027. Conception is estimated at 24 April 2026, which is day 8 of the third lunar month. She was born the day before Chinese New Year 1990, so she was born in the lunar year 1989, and her lunar age at conception is 2026 − 1989 + 1 = 38. Her age plus one would give 37, the wrong row.

Lunar months and leap months

Lunar calendar gender prediction depends on the Chinese month, not the calendar month. Chinese months begin at a new moon, so they do not line up with January to December, and Chinese New Year falls between 21 January and 20 February. About seven years in every nineteen have a thirteenth month, a leap month that repeats the number of the month before it. The chart has no column for a leap month. The common rule, which this calculator follows, reads days 1 to 15 of a leap month as that month and days 16 onward as the next. Dates are converted with the Hong Kong Observatory's Gregorian–lunar tables, which run from 1940 to 2060.

Gender prediction by due date or last period

Most people do not know the day of conception, so the calculator estimates it: 266 days before the due date, or the first day of the last period plus the cycle length minus 14 days. Those estimates are uncertain by several days. If the estimated window crosses the start of a lunar month or Chinese New Year, the chart can give two answers, and the calculator shows both. Many sites skip the conversion and read the chart with calendar months or with age plus one, so a user who checks two sites can get two answers from the same chart.

Why Chinese gender charts differ

Two charts are in circulation. The one used here is the version most English-language sites publish; we compared six of them and took the majority reading in the five cells where they differ. The version published in Chinese, known as the Qing palace table, differs from it in 144 of the 336 cells. Neither can be traced to an original, and there is no reason to expect either to do better than chance.

Where the chart comes from

The stories told about the chart are legend. One says it was found in a royal tomb near Beijing about 700 years ago; another says it was made for the Qing court, which began in 1644, so the two cannot both be true. A third says the original is kept at an institute of science in Beijing. No source names a museum, a catalogue number, a publication or a scholar behind any of them, and a historian of Chinese medicine asked about the Qing story found no evidence for it. There is no evidence that the chart is old.

How accurate is the Chinese gender predictor?

It predicts a baby's sex no better than chance. Researchers from the University of Michigan and the Karolinska Institute applied the chart to 2,840,755 births in Sweden between 1973 and 2006. The predicted sex agreed with the baby's sex no more often than a coin toss would, whatever the mother's age, the year, or the way the dates were converted (Villamor and colleagues, 2010). A baby's sex is set at fertilization, by whether the sperm carries an X or a Y chromosome, and the calendar has no bearing on it.

Reliable ways to find out the baby's sex

• A blood test from 10 weeks. Cell-free DNA screening, often called NIPT, can report the baby's sex from about 10 weeks of pregnancy. It is highly accurate but not certain. In the UK the NHS offers it only after a higher-chance screening result, and the NHS test does not report sex; private tests do. Tests offered before 7 weeks, and urine tests, are not reliable.
• The mid-pregnancy scan. In the US, the anatomy scan at 18 to 22 weeks can usually show the sex. In the UK, sex is not part of the 20-week screening scan (18 to 21 weeks), and whether the sonographer will say depends on the hospital's policy.
• Not by invasive testing. Chorionic villus sampling and amniocentesis are diagnostic tests offered for medical reasons, and each carries a small risk of miscarriage, about 1 in 200 or lower (NHS). They are not done to learn the sex.