Chinese gender calendar

How the Chinese gender calendar works

The Chinese gender calendar is a lookup table: cross-reference the mother's lunar age at conception with the lunar month she conceived in, and the chart returns “boy” or “girl.” There's no underlying math — just a fixed table that's been passed down for centuries.

Tradition holds that a copy of the chart was buried in a Beijing tomb around 700 years ago, and that the modern version was recovered there. Historians have never confirmed this origin story, but variants of the chart circulate widely in Chinese tradition and now globally.

The version on this page (and in the chart below) is the standard 28-by-12 table that appears across virtually every English-language Chinese-calendar tool — babycenter, whattoexpect, americanpregnancy, and others all use the same one.

The lunar age and lunar month, simplified

The chart wants two inputs: the mother's lunar age at conception (rows 18–45) and the lunar month of conception (columns 1–12). These don't map perfectly to the Gregorian calendar most people use.

Lunar age in Chinese tradition is roughly your Gregorian age plus one — at birth you're counted as one year old. The strictly accurate calculation also accounts for whether your birthday has passed in the current lunar year, which depends on when Lunar New Year falls (late January through mid-February). For folklore purposes, almost every calculator uses the simple plus-one approximation — including this one.

Lunar months are 29–30 days long and start with the new moon. Strict lunar conversion would shift some edge-of-month dates into a different column. In practice, most calculators use the Gregorian month number directly, which is close enough for tradition's purposes.

The disagreement between strict and simplified versions is itself a tell: if the method were medically accurate, the chart would have one canonical version everyone agreed on.

How accurate is the Chinese gender calendar?

Honestly: about as accurate as flipping a coin.

The largest published study — Yang 2010 in the Canadian Medical Association Journal — applied the chart to a real cohort of pregnancies and found accuracy of about 50%. Subsequent studies have replicated that result: there's no biological mechanism connecting lunar age or conception month to the chromosome of the fertilizing sperm.

The chart feels accurate to a lot of people for two reasons. First, there are only two possible answers, so it's right half the time by definition. Second, people tend to remember the times tradition was right and forget the times it wasn't. That's confirmation bias, not evidence.

The chart is fun to try; it's a long tradition; many parents enjoy it. None of that makes it predictive. Use the result as folklore — don't paint a nursery on the basis of it.

When you want to know for certain

Three medical methods reliably determine biological sex during pregnancy:

• NIPT (non-invasive prenatal testing) — a blood draw from the mother that detects fetal DNA. Reliable from about 9–10 weeks of gestation onward; over 99% accurate for sex when enough fetal DNA is present.
• Mid-pregnancy anatomy ultrasound — typically between 18 and 22 weeks. Very accurate when the baby cooperates and a clear view is available.
• Amniocentesis or chorionic villus sampling (CVS) — definitive, but only offered when there's a medical reason because both carry a small miscarriage risk.

If knowing your baby's sex matters, talk to your healthcare provider about which option is appropriate for your pregnancy and timeline.

Other traditional methods

The Chinese calendar isn't the only old-wives'-tale method floating around. Others include the Mayan parity prediction (based on mother's age and conception year), the ring test, the baking-soda test, the heart-rate predictor, and a long list of parent-traits signals (cravings, morning-sickness severity, how you're carrying). All perform at chance level when properly studied. If you want to try several side by side, our multi-method baby gender predictor runs the Chinese calendar, the Mayan method, and a parent-traits scorer in one tool.

Frequently asked questions

Sources and further reading

• Wikipedia — Chinese gender predictor chart
• Canadian Medical Association Journal — Predicting fetal sex by maternal age and conception month using a Chinese lunar calendar (Yang, 2010)
• ACOG — Prenatal genetic screening tests — Frequently Asked Questions
• Mayo Clinic — Noninvasive prenatal testing overview