Conception Date Calculator

When Did Conception Occur?

Conception typically occurs around ovulation, which is about 14 days before the next expected period. From a due date, subtract 266 days to estimate conception.

This is an estimate. Sperm can survive up to 5 days, so conception could have occurred several days before or on the day of ovulation.

Conception date is estimated by working backward from a known due date: subtract 266 days (38 weeks) from the EDD. Alternatively, it typically occurs 14 days after the first day of the last menstrual period (for a 28-day cycle). For IVF, the fertilization date is known exactly — conception occurred on that date in the lab.

Why conception date matters: knowing the approximate conception date helps confirm the accuracy of gestational age if LMP is uncertain. It also matters for paternity timeline questions and, in some medical situations, for determining which week-specific fetal development stages applied at a given time.

Conception is not instantaneous: sperm can survive in the female reproductive tract for up to 5 days. The egg remains viable for approximately 12–24 hours after ovulation. The "conception date" typically means the date the egg was fertilized, but conception could be from intercourse occurring up to 5 days before ovulation.

Implantation: fertilized egg implantation occurs approximately 6–12 days after ovulation (most commonly day 8–10). A home pregnancy test can detect hCG 1–2 days after implantation — typically around 10–14 days after ovulation (or "days past ovulation," DPO). Testing before day 10 DPO risks a false negative even in an ongoing pregnancy.

This calculator provides estimates based on standard cycle assumptions. Consult a healthcare provider for pregnancy confirmation and accurate dating.

See also: Ovulation Calculator · Due Date Calculator