Conception Calculator

Ovulation, and likely conception, typically occurs about 14 days after the first day of your last period in a standard 28-day cycle, adjusted for your actual average cycle length.

Conception is estimated at 266 days before the due date (38 weeks of gestation from conception, following Naegele's rule for a 280-day pregnancy from the last period).

Sperm can survive in the body for up to five days, so conception could happen anywhere in a several-day fertile window around ovulation, not just on the ovulation day itself.

An early dating ultrasound (ideally in the first trimester) gives the most accurate estimate of gestational age and therefore conception timing.