Chinese Gender Chart Methodology

This page documents the math and the evidence behind the DueDateLab Chinese Gender Chart. The tool is offered as entertainment. Peer-reviewed studies have shown that the chart predicts baby sex at approximately chance, about 50 percent. This page exists for transparency: anyone can see the formula and the evidence for the accuracy claim.

Open the Chinese Gender Chart →

Summary

The tool takes the mother's date of birth and the month of conception, computes the mother's lunar age at conception, and looks up the predicted sex in the traditional Qing-dynasty-attributed chart. The output is a single predicted sex. The tool does not claim accuracy; it labels itself as entertainment and links to the peer-reviewed evidence that the method performs at chance.

Formula 1, lunar age at conception

Lunar age, also called Chinese age or nominal age, treats the prenatal period as year one. For a mother born on date B conceiving on date C:

Lunar age = Western age at C + 1, if C falls on or after the Chinese New Year that precedes C in the Western calendar year
Lunar age = Western age at C + 2, if C falls before that Chinese New Year but the mother's lunar birthday has not yet arrived that lunar year

The calculator uses a table of Chinese New Year dates from 1950 through 2075 to resolve the lunar year transition correctly. This is the standard approach in published versions of the chart.

Formula 2, chart lookup

The chart is a two-dimensional lookup, rows indexed by lunar age 18 through 45, columns indexed by lunar month of conception 1 through 12. The cell value is "boy" or "girl". The specific values used are the traditional values widely cited in English-language pregnancy references and match the chart displayed on the tool page. The lunar month of conception is derived from the Western conception date via the same Chinese New Year table used for lunar age.

Input validation

• Mother's date of birth. Must be in the last 80 years and at least 14 years before today.
• Conception date. Must be within the last 300 days or up to 14 days in the future (to accommodate planning scenarios).
• Lunar age bounds. The chart is defined for lunar ages 18 to 45. Ages outside this range trigger a warning and fall back to a plain-English note that the chart has no value for that age.

Outputs

• Predicted sex (boy or girl).
• Mother's lunar age at conception.
• Lunar month of conception.
• Accuracy disclaimer stating that peer-reviewed studies put the chart at chance, with a link to the evidence.

Accuracy

A 2010 Swedish population study (Villamor et al.) analyzed 2,840,755 singleton births between 1973 and 2006 and reported a kappa statistic of 0.0002 (95% CI -0.0009 to 0.0014) between predicted and actual sex, statistically indistinguishable from chance. On a binary outcome, that kappa corresponds to about 50 percent accuracy. Non-invasive prenatal testing (NIPT) from a maternal blood draw is available from about 10 weeks and can screen for sex chromosomes as part of aneuploidy screening (ACOG, Prenatal Genetic Screening Tests). A mid-trimester anatomy ultrasound at 18 to 22 weeks is the standard time for sex determination (ACOG, Ultrasound Exams). For any clinical or personal decision, we recommend one of those tools, not the chart. See our article Chinese Gender Chart Accuracy for the full discussion.

Privacy of calculations

All computation runs client-side in JavaScript. Mother's date of birth and conception date never leave the browser, are never stored in a cookie or local storage, and are never transmitted to a DueDateLab server or a third-party server. Analytics on the rest of the site are covered by the privacy policy, but the tool page itself collects no input data.

Sources

Authorship

The DueDateLab Editorial team writes and maintains this page. This tool is entertainment, not medical, and no clinical claim is made. Accuracy statements are sourced from the peer-reviewed citations above. DueDateLab is published from Belgium.

Conflicts of interest. DueDateLab is supported by advertising and may use affiliate links. Advertising and affiliate relationships do not influence the methodology, sources, or accuracy claims on this page. Any sponsored content is clearly labeled.

Last updated May 15, 2026.