What the chart claims to do
The method examined by Villamor and colleagues combines maternal lunar age with conception month and assigns a predicted sex using an algorithm. That is a prediction rule, not an observation of a particular pregnancy. A calendar conversion supplies dates; the additional step assigning a sex requires its own evidence.
When discussing a grid with family, ask which version they have and what each axis means. Save its instructions alongside the image. Do not silently substitute today’s age for an age requested at another date, or Gregorian July for lunar month seven. These checks clarify what the chart is saying; they do not validate it.
What the primary validation study found
The 2010 population study by Eduardo Villamor, Louise Dekker, Tobias Svensson and Sven Cnattingius used 2,840,755 singleton births in Sweden from 1973 to 2006. Overall agreement beyond chance, measured by kappa, was 0.0002, with a 95% confidence interval of −0.0009 to 0.0014. The authors concluded that the tested method was no better than chance.
The publisher’s abstract also reports a 1,000-birth validation subset using a website-customised lunar-date algorithm, again without useful agreement. This was a test in a specified population of a specified method. It supplies no demonstrated medical predictor and does not provide a probability for your individual pregnancy. The primary-source link below identifies the paper; our source review accessed the complete publisher abstract, not a full-text clinical review.
Choose an age convention before calculating
Our Chinese age tool uses a declared nominal-age rule: one in the birth lunar year, then another year at each Lunar New Year. Its formula is the reference lunar year minus the birth lunar year, plus one. International age instead counts completed Gregorian birthdays. Write the convention beside the number so another reader can reproduce your calculation.
For a mother’s age on a known reference date, enter her Gregorian birth date and that reference date. An age today answers a different question from an age at an earlier recorded event. If the reference date is unknown, leave that uncertainty visible. An age calculation cannot discover a conception date, and this guide does not estimate one.
Convert a date without changing its meaning
Hong Kong Observatory explains that the Chinese agricultural calendar combines lunar months with a solar year and uses leap months. A lunar month number therefore is not a Gregorian month number. A lunar birth record needs a year, month, day and any regular-or-leap designation before conversion. Keep the original record as well as the converted date.
Use the calendar converter first when your starting record is lunar; the age tool expects a Gregorian birth date. Check the tool’s supported range and validation messages. A leap month repeats a month designation; it does not mean adding another year to someone’s age. If a handwritten record leaves the designation unclear, ask for clarification instead of selecting the date that produces a preferred answer.
Compare a calendar fact with a prediction claim
Consider a record dated February 16, 2026 and another dated February 17, 2026. Under the declared age convention, the Lunar New Year boundary changes the nominal-age count. That is a reproducible statement about calendar years. Adding a boy-or-girl label is a separate prediction rule and does not follow from the date arithmetic.
When reading a published chart as a cultural text, record its title, publication date, axes and instructions. Compare those features rather than assigning it a verified ancient provenance. The study cited here evaluates predictive agreement; it does not authenticate the origin of every grid circulating online.
A useful next step depends on your question
For calendar research, note the birth date, reference date, original calendar and age convention. Then use the two linked tools to check the conversion and count. For a family conversation, ask whether the person wants help reading a record or is asking for a prediction. Those requests can sound similar while needing different responses.
A new year printed above a chart does not establish new predictive evidence. Keep one durable explanation rather than treating annual chart versions as independent methods. We do not authenticate stories about royal tombs or imperial origins here: no verified provenance is needed to explain the calculation, and an appealing origin story would not establish predictive accuracy.
A useful distinction
A correct lunar-date conversion does not validate a baby-sex prediction attached to it.
Frequently asked questions
3 common questions
- Is lunar age always ordinary age plus one?
- No. Use complete birth and reference dates and state the rule. The site’s calculator counts lunar-year boundaries and shows completed Gregorian age separately; substituting a fixed extra year can give a different result.
- Can the Chinese age calculator answer the baby-sex question?
- No. It supplies nominal age, international age and lunar-year references. It does not output a sex prediction, infer conception or assess a pregnancy.
- What should I do if two gender charts disagree?
- Record their different assumptions if you are comparing the charts as texts. Do not choose whichever result you prefer or treat agreement between charts as confirmation. For a date question, return to the original dated record.
Sources & further reading
- Villamor et al. (2010): population validation, publisher abstractPaediatric and Perinatal Epidemiology · WileyAccessed Find an archived copy
- The Chinese Agricultural Calendar: lunar months and solar yearsHong Kong ObservatoryAccessed Archived copy ·