Due Date October 10: When Did You Conceive?
Counting back from a October 10 due date puts the most likely day of conception at January 17. That's an estimate, so we've also included the window of days around it.
Key dates for a October 10 due date
| Most likely conception date | January 17 |
|---|---|
| Likely conception window | January 14 – January 20 |
| Days when sex could have led to pregnancy | January 12 – January 18 |
| Estimated first day of last period | January 3 |
| Positive home test likely from | January 31 (around the missed period) |
| Second trimester begins (14 weeks) | April 11 |
| Third trimester begins (28 weeks) | July 18 |
| Full term begins (39 weeks) | October 3 |
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 October 10 gives January 17.
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?
Due dates set from an early ultrasound are usually more accurate than those set from a period date alone, so if your provider changed your due date after a scan, use the newer one here.
If your cycles are usually longer than 28 days, conception probably happened a little later than January 17; 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.