Conception is a numbers game with a narrow window. Knowing exactly which days matter — and why they matter — turns a vague 'try around the middle of the month' into a plan with real precision.
Why the window is longer than ovulation
The egg survives only about 24 hours, but sperm can live 3–5 days in the reproductive tract. That asymmetry is why the fertile window stretches backward: sperm arriving before ovulation can wait for the egg.
Building the window from your cycle
Ovulation happens roughly 14 days before the next period. Counting back from that point creates the window — 5 days before through 1 day after — which this calculator maps to calendar dates for you.
Refining with real signals
Calendar estimates assume regularity. Ovulation kits, temperature tracking and cervical mucus signs turn the estimate into confirmation, catching the month-to-month variation most cycles have.
Frequently asked questions
It's the days when intercourse can result in pregnancy: about 5 days before ovulation plus the day after, because sperm survive several days while an egg lives about 24 hours.
Peak fertility is on ovulation day itself, when the egg is released. The days just before it are also high-fertility days.
Aiming for intercourse every 1–2 days across the whole fertile window maximises the chance of conception while keeping it manageable.