How ovulation calculator works
Ovulation is the release of an egg from your ovary, and it usually happens about 14 days before your NEXT period starts. Working backwards from a predictable luteal phase of ~14 days, this calculator estimates your ovulation date as your next period minus 14 days, where your next period is the first day of your last period (LMP) plus your cycle length.
The fertile window is the handful of days each cycle when pregnancy is possible. Sperm can survive up to about 5 days inside the reproductive tract, and the egg lives about 24 hours after ovulation. So the fertile window runs from 5 days before ovulation through 1 day after — about 7 days total. Having intercourse in this window maximises the chance of conception.
Enter the first day of your last period, your average cycle length (and period length), and how many future cycles to predict. The tool lists each upcoming cycle’s predicted period start, ovulation date, and fertile window so you can plan for either trying to conceive or avoiding pregnancy. This is an estimate based on average cycles, not contraception or medical advice — real cycles vary.