Due Date September 7: When Did You Conceive?
A due date of September 7 points back to a conception date of about December 15 of the previous year. Below you'll find the full set of dates that go with it, from your estimated last period to the start of each trimester.
Key dates for a September 7 due date
| Most likely conception date | December 15 |
|---|---|
| Likely conception window | December 12 – December 18 |
| Days when sex could have led to pregnancy | December 10 – December 16 |
| Estimated first day of last period | December 1 |
| Positive home test likely from | December 29 (around the missed period) |
| Second trimester begins (14 weeks) | March 9 |
| Third trimester begins (28 weeks) | June 15 |
| Full term begins (39 weeks) | August 31 |
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 7 gives December 15.
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?
A due date is a planning estimate rather than a promise. Most babies arrive within two weeks either side of it, which is why any conception date calculated from it is a best guess.
If your cycles are usually longer than 28 days, conception probably happened a little later than December 15; 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.