Chinese Gender Calendar by Due Date

Why the chart needs a conception date at all

The Chinese gender chart has exactly two inputs: the mother’s lunar age and the lunar month she conceived in. Nothing in it refers to the due date or the birth. So a due date is not a substitute input; it is a way of working out the input the chart actually wants.

The 266-day rule

An average pregnancy runs 266 days from conception. You will more often see the figure 280 days, and both are correct; they are just measured from different starting points:

• 280 days is measured from the first day of your last menstrual period, which is roughly two weeks before conception.
• 266 days is measured from conception itself.

Using 280 by accident places your conception date a fortnight too early. Near a lunar month boundary that is enough to shift you into the wrong column of the chart, so it is worth getting right. If you would rather start from your period date instead, use the LMP method, which adds 14 days rather than subtracting 266.

Worked example

Take a mother born on 15 June 1995 with a due date of 1 December 2026:

1. Subtract 266 days from the due date → conception on 10 March 2026.
2. Convert that to the lunar calendar → lunar month 1.
3. Convert her birth date the same way and count her lunar age at conception → 32.
4. Read row 32, column 1 of the chart → Boy.

Every number there comes from the same code that powers the calculator above, so you can check it yourself by entering those two dates. See row 32 on the chart.

Due dates through 2026, converted

A quick reference showing how due dates across the year map back to conception dates and their lunar months. Note how the lunar month does not track the Western month, which is the whole reason this conversion matters.

Where this method is weakest

We would rather tell you this than have you over-trust the result. Your due date is itself an estimate, and its accuracy depends on how it was set:

• Set by a first-trimester dating scan: usually accurate to within a few days, so the conception date you get here will be close.
• Calculated from your last period: this assumes a 28-day cycle with ovulation on day 14. If your cycles run longer or shorter, the real conception date moves by the same number of days.

If your conception date lands within a few days of a lunar month boundary, try the dates either side in the calculator and see whether the answer changes. If it does, treat the result as genuinely uncertain, which, given the chart is folklore anyway, is the honest position.