Last updated: March 2026
When Did I Conceive?
Conception occurs when a sperm cell fertilizes an egg, typically during ovulation — about 14 days before your next expected period. This means in a standard 28-day cycle, ovulation happens around day 14. In a 32-day cycle, it shifts to around day 18.
The fertile window spans about 6 days — the 5 days before ovulation plus the day of ovulation itself. Sperm can survive in the reproductive tract for up to 5 days, while the released egg is viable for only 12-24 hours.
This means conception doesn't necessarily happen on the day you had intercourse. If you had intercourse 3 days before ovulation, the sperm could have waited and fertilized the egg when it was released.
For women who track their cycles with basal body temperature or ovulation prediction kits, the conception date can be estimated more precisely. Without tracking, the calculator uses cycle length to estimate the likely ovulation date.
IVF and other fertility treatments provide the most precise conception timing because the embryo transfer date and embryo age are known exactly, eliminating the guesswork involved with natural conception dating.
Frequently Asked Questions
When did I conceive?
Conception typically occurs about 14 days after the first day of your last menstrual period, during ovulation. If you have a 28-day cycle and your last period started March 1, you likely conceived around March 15.
Can I know the exact date of conception?
Unless you used fertility treatments like IVF, the exact conception date is an estimate. Sperm can live inside the body for up to 5 days, and the egg is viable for 12-24 hours after ovulation, creating a fertile window of about 6 days.
How does cycle length affect conception date?
In a 28-day cycle, ovulation typically occurs on day 14. In a 35-day cycle, ovulation shifts to around day 21. The calculator adjusts based on your cycle length to estimate when conception likely occurred.
Is conception date the same as the date I had intercourse?
Not necessarily. Because sperm can survive for up to 5 days, conception could have occurred several days after intercourse. The conception date refers to when the sperm fertilized the egg.
Why does gestational age start before conception?
Gestational age is counted from the first day of your last period, about 2 weeks before conception. This convention exists because the last period date is more reliably known than the exact conception date.