Due Date September 22: When Did You Conceive?
If your baby is due on September 22, conception most likely happened around December 30 of the previous year. Here is how that date is worked out and the range of days it could realistically fall on.
Key dates for a September 22 due date
| Most likely conception date | December 30 |
|---|---|
| Likely conception window | December 27 – January 2 |
| Days when sex could have led to pregnancy | December 25 – December 31 |
| Estimated first day of last period | December 16 |
| Positive home test likely from | January 13 (around the missed period) |
| Second trimester begins (14 weeks) | March 24 |
| Third trimester begins (28 weeks) | June 30 |
| Full term begins (39 weeks) | September 15 |
How the conception date is calculated
Due dates are normally counted as 280 days (40 weeks) from the first day of the last menstrual period. In a typical 28-day cycle, ovulation and conception happen about two weeks after that period starts, so conception sits roughly 266 days before the due date. Subtracting 266 days from September 22 gives December 30.
Sperm can survive in the reproductive tract for up to five days, while an egg lives for about 12 to 24 hours after ovulation. That means sex several days before ovulation can still lead to pregnancy.
How certain is this date?
Only a small share of babies, often quoted at around 4 to 5 percent, arrive on their exact due date, so dates worked backwards from a due date carry a margin of a few days either way.
If your cycles are usually longer than 28 days, conception probably happened a little later than December 30; with shorter cycles, a little earlier. A cycle that is 32 days long, for example, shifts the likely date about four days later.
Check your own dates
Enter your exact due date in the conception date calculator to see these results with weekdays and the correct year, or start from your last period with the last-period conception calculator.
Conception Date Calculator: Find the most likely conception date from your due date.
Open the calculatorThis article is general information, not medical advice. Talk to a doctor or midwife about your own pregnancy or fertility.