One traditional tool, several names
Chinese gender predictor, Chinese gender calendar and Chinese birth chart often refer to this same folklore lookup. Here, “birth chart” means the age-and-month table, not an astrological chart based on a birth time. The calculator and printable calendars all use the same table.
Start with regular calendar dates
Enter the mother’s date of birth and an estimated conception date using the familiar Gregorian calendar. You do not need a lunar birthday, manually adjusted age, or separate Chinese calendar.
If you know only the due date, choose that option. We subtract 266 calendar days to estimate conception, reflecting the average interval described in the MSD Manual’s explanation of due dates. This does not establish the actual day conception happened.
Convert to the lunar calendar
We use lunar-javascript to find the lunar year of birth, lunar year of conception and lunar conception month. Inputs are treated as calendar dates without a time of day, so your browser’s time zone does not move a date to the preceding day.
The converter uses the Chinese calendar represented by the library. Lunar months begin at calendar-defined boundaries and do not line up with Gregorian months. Lunar month 1 is not another name for January.
Calculate traditional lunar age
The convention used here counts one year at birth and adds a year at each Chinese New Year. It uses Chinese New Year, not the solar term known as Start of Spring.
Conception lunar year − birth lunar year + 1
This is why “regular age + 1” is not always the same calculation. Check a specific date with the Chinese lunar age calculator.
A complete example
For a birth date of June 15, 1995 and conception date of May 1, 2026:
- The lunar birth year is 1995.
- Conception is lunar year 2026, month 3, day 15.
- Lunar age is 2026 − 1995 + 1 = 32.
- Age 32 and month 3 intersect at “Boy” in this chart.
This is a worked lookup, not evidence about an actual pregnancy. “Try an example” on the homepage uses these dates. A due date of January 22, 2027 also leads to this example after subtracting 266 days. The relevant reference is the 2026 conception calendar.
Which chart do we use?
We use the 18-to-45 age, 12-month matrix from the MIT-licensed bdp-raymon/chinese-gender-prediction project, pinned to revision 8c5338d. We reuse its table, not its age-calculation code. License and attribution are included.
Different versions of this chart circulate. We have not verified claims that any one version is an original imperial or archaeological record. We do not describe it as an official or medically approved chart.
The same data drives the visible chart and the calculator. Ages outside the chart range are rejected rather than silently changed to the nearest supported age.
What happens in a leap month?
The Chinese calendar sometimes contains an extra month with the same number as another month. The 12-column chart has no separate leap-month column.
Our convention: a leap month uses the column with the matching number. Leap month 6 uses column 6. Results identify the leap month. Other traditional interpretations may use different rules, so calculators can disagree.
Why we flag uncertain dates
If conception is within seven days of a lunar-month boundary, we show a notice. Seven days is a usability reminder, not a medical confidence interval. A small change in your estimate may move the lookup to another cell.
Dates remain in your browser. No calculation needs an account or remote service. Read how data is handled.
Conversion is not scientific prediction
A repeatable lookup can describe a tradition without scientific predictive value. Our accuracy guide separates the calendar calculation from the claim it is sometimes used to make.
Method and sources checked October 9, 2026.