Ovulation Calculator

How the Ovulation Calculator works

Ovulation is estimated as 14 days before your next expected period, regardless of cycle length — a standard assumption since the luteal phase (the days between ovulation and your next period) stays fairly constant from cycle to cycle, while the follicular phase before it (period to ovulation) is what actually varies. That 14-day offset is why a longer or shorter cycle shifts your ovulation date but not the gap between ovulation and your next period. The calculator distinguishes two windows around that estimate. The "ovulation window" (±2 days around the estimated date) covers the likely range for the egg's release. The "intercourse window" opens earlier — 5 days before ovulation — because sperm can survive in the reproductive tract for up to five days and still fertilize an egg released near the end of that window, while the egg itself is typically viable for only about 24 hours after release. The pregnancy test date is set 5 days before your next expected period, which is the earliest point a sensitive test can realistically pick up rising hCG for most people — testing on or after your missed period is more reliable if you can wait. The due date, if this cycle results in a pregnancy, uses the standard 280-day (40-week) estimate from the first day of your last period (Naegele's rule), the same convention used to compute a due date on the Pregnancy Calculator.