How is conception date estimated?
Conception can be estimated by subtracting 266 days from a due date, or by estimating ovulation from the last period date and average cycle length.
Why conception date is only an estimate
Ovulation timing varies, and sperm can survive for several days. That means conception timing is best treated as a possible date or window, not a confirmed date.
What is the fertile window?
The fertile window is the estimated range around ovulation when pregnancy is more likely. This calculator shows five days before the estimated conception date through one day after.