People trying to conceive often focus on a single "ovulation day" — but the actual window of opportunity is several days wide, for a specific biological reason.
Fertile window calculator, why it starts before ovulation
Sperm can survive inside the body for up to 5 days, while the egg is only viable for about 24 hours after release. That asymmetry is why the fertile window includes the 5 days before ovulation, not just the day itself.
Ovulation date from last period, the calculation
For a 28-day cycle starting August 1, ovulation is estimated at day 14 of the cycle — August 15 — assuming the typical 14-day luteal phase (the time between ovulation and the next period). That puts the fertile window at August 10 through August 15.
Conception calculator, the same underlying math
A separate "conception calculator" asking the same question — when am I most likely to conceive — runs the identical last-period-plus-cycle-length calculation, which is why this tool covers both under one name.
