When Did I Conceive if My Due Date Is November 20?
Wondering when your November 20 baby was conceived? Using the standard 266-day rule, the answer is most likely February 27, give or take a few days.
Key dates for a November 20 due date
| Most likely conception date | February 27 |
|---|---|
| Likely conception window | February 24 – March 2 |
| Days when sex could have led to pregnancy | February 22 – February 28 |
| Estimated first day of last period | February 13 |
| Positive home test likely from | March 13 (around the missed period) |
| Second trimester begins (14 weeks) | May 22 |
| Third trimester begins (28 weeks) | August 28 |
| Full term begins (39 weeks) | November 13 |
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 November 20 gives February 27.
Conception happens when sperm meets the egg, usually within a day of ovulation. Since sperm may wait up to five days for an egg to be released, the window for sex that could have caused the pregnancy is wider than a single day.
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 February 27; 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.