The Chinese gender chart asks for the month of conception. That's the most common place people go wrong: they enter the due date, the month of a positive test, or the baby's expected birthday. Here's how to get a reasonable estimate.
These are general rules of thumb, not medical advice. Your clinician's dating scan is the most reliable estimate of when a pregnancy began.
1. From your last menstrual period (LMP)
Pregnancy is conventionally dated from the first day of your last period, but conception usually happens around ovulation — about two weeks later in a 28-day cycle.
Estimate: first day of LMP + 14 days. If your cycles are longer or shorter than 28 days, ovulation typically shifts by the same amount (for a 32-day cycle, try LMP + 18 days).
2. From your due date
A standard due date is 280 days after LMP, which is about 266 days (38 weeks) after conception.
Estimate: due date − 266 days. If your due date was revised after an early ultrasound, use the revised one.
3. From ovulation tracking
If you used ovulation tests, basal body temperature or cycle-tracking apps, the likely conception window is the day of ovulation and the day or two before it. Use the ovulation date.
4. From an IVF or embryo transfer
Clinics usually date IVF pregnancies from the transfer. For a day-5 blastocyst transfer, the equivalent "conception" date is roughly transfer date − 5 days; for a day-3 transfer, transfer date − 3 days. Ask your clinic if unsure.
When does the exact day matter?
Usually it doesn't — the chart only cares about the lunar month. It matters when your estimate falls near a lunar month boundary. Lunar months start on the new moon, so they begin on a different Gregorian date each month (for 2027, see the 2027 calendar).
If you're not sure, use our predictor with "I only know the month". It checks every day of that Gregorian month and, if the month spans two lunar months with different chart cells, shows both date ranges instead of quietly picking one.
Quick reference
| You know | Estimate of conception |
|---|---|
| First day of last period (28-day cycle) | LMP + 14 days |
| Due date | Due date − 266 days |
| Ovulation date | That date |
| Day-5 embryo transfer | Transfer − 5 days |
| Day-3 embryo transfer | Transfer − 3 days |
Curious what researchers found when they tested the Chinese gender chart? Read Is the Chinese gender chart accurate?.
