When Did I Conceive if My Due Date Is April 15?
If your baby is due on April 15, conception most likely happened around July 23 of the previous year. Here is how that date is worked out and the range of days it could realistically fall on.
Key dates for a April 15 due date
| Most likely conception date | July 23 |
|---|---|
| Likely conception window | July 20 – July 26 |
| Days when sex could have led to pregnancy | July 18 – July 24 |
| Estimated first day of last period | July 9 |
| Positive home test likely from | August 6 (around the missed period) |
| Second trimester begins (14 weeks) | October 15 |
| Third trimester begins (28 weeks) | January 21 |
| Full term begins (39 weeks) | April 8 |
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 April 15 gives July 23.
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?
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 July 23; 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.