How the Chinese Gender Calendar Works

1. Calculate lunar age at conception.

Use the mother’s traditional nominal age on the conception date—not her current age or Western age.

In this system, a newborn is counted as age one. Everyone’s nominal age increases at Chinese New Year rather than on individual birthdays. Our formula is:

A person born before Chinese New Year belongs to the previous lunar year. A conception before Chinese New Year likewise belongs to the previous lunar year. Converting both complete dates first handles both boundaries without a shortcut.

2. Convert the conception month.

The chart columns are Chinese calendar months 1–12. They do not correspond directly to January–December. Traditional months have 29 or 30 days and begin on different Gregorian dates each year.

We convert the complete Gregorian conception date with lunar-javascript, then apply checked Hong Kong Observatory overrides for official coverage years. The result includes the lunar year, month, day, and leap-month flag.

Leap-month convention

A leap month repeats the preceding regular month number. Since the standard table has no thirteenth column, this site maps a leap month to the same numbered regular column. Leap month 6 therefore uses month 6. This is a stated modern chart convention, not a universally proven historical rule.

3. Read the traditional table.

Choose the row for lunar ages 18–45 and the column for lunar months 1–12. The intersection says Boy or Girl. If the lunar age is outside 18–45, this version of the chart has no row and our calculator says so rather than guessing.

The table is fixed across Gregorian years. Annual calendars only change the conversion from a Gregorian date to a traditional month.

When the exact conception date is unknown.

• Last menstrual period: add 14 days to the first day of the LMP. This is a common estimate, but ovulation does not occur on day 14 for everyone.
• Estimated due date: subtract 266 days. Use the current due date supplied by a healthcare professional; different dating methods and revisions can change the estimate.
• IVF / embryo transfer: following the reference chart convention, we use the transfer date as the lookup date. Embryo transfer and biological fertilization are not necessarily the same event or date.

All three involve assumptions. If an estimated date is close to a lunar-month boundary, the calculator displays an additional warning because a small date change may alter the chart column.

A verified example.

Suppose the mother was born on 5 October 1994 and the estimated conception date is 10 June 2026.

1. Her birth date belongs to Chinese calendar year 1994.
2. 10 June 2026 also belongs to Chinese calendar year 2026.
3. Lunar age is 2026 − 1994 + 1 = 33.
4. 10 June 2026 falls in Chinese calendar month 4, on day 25.
5. Row 33 and column 4 contain the traditional label Boy.

This example verifies the chart lookup, not the baby’s actual biological sex. A correct folklore calculation is still not a scientific prediction.

Common mistakes to avoid.

• Using Western age instead of lunar age at conception.
• Using a Gregorian month number as the chart column.
• Using the due date directly instead of estimating conception.
• Forgetting that January or early February may belong to the previous lunar year.
• Assuming every source uses the same leap-month rule or chart variant.
• Treating a correctly calculated folklore label as medical information.