Due Date December 3: When Did You Conceive?
If your baby is due on December 3, conception most likely happened around March 12. Here is how that date is worked out and the range of days it could realistically fall on.
Key dates for a December 3 due date
| Most likely conception date | March 12 |
|---|---|
| Likely conception window | March 9 – March 15 |
| Days when sex could have led to pregnancy | March 7 – March 13 |
| Estimated first day of last period | February 26 |
| Positive home test likely from | March 26 (around the missed period) |
| Second trimester begins (14 weeks) | June 4 |
| Third trimester begins (28 weeks) | September 10 |
| Full term begins (39 weeks) | November 26 |
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 December 3 gives March 12.
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 March 12; 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.