Due on July 31? Your Most Likely Conception Date
Wondering when your July 31 baby was conceived? Using the standard 266-day rule, the answer is most likely November 7 of the previous year, give or take a few days.
Key dates for a July 31 due date
| Most likely conception date | November 7 |
|---|---|
| Likely conception window | November 4 – November 10 |
| Days when sex could have led to pregnancy | November 2 – November 8 |
| Estimated first day of last period | October 24 |
| Positive home test likely from | November 21 (around the missed period) |
| Second trimester begins (14 weeks) | January 30 |
| Third trimester begins (28 weeks) | May 8 |
| Full term begins (39 weeks) | July 24 |
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 July 31 gives November 7.
Because sperm can live for up to five days, the act of sex and the moment of conception aren't always the same day. Fertilisation happens close to ovulation, but the sex that led to it may have been days earlier.
How certain is this date?
Remember that a due date is only the midpoint of a range. Ovulation timing varies from cycle to cycle, so the true conception day can sit a few days away from the estimate.
If your cycles are usually longer than 28 days, conception probably happened a little later than November 7; 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.