Ovulation Calculator
Find your most fertile days and plan around your cycle.
This estimate assumes a ~14-day luteal phase. Cycles vary, so treat it as a guide. For trying-to-conceive or contraception decisions, talk to your doctor.
Questions, answered
How is my fertile window calculated?
We estimate ovulation as 14 days before your next expected period (the luteal phase is fairly consistent). Your fertile window is the 5 days before ovulation plus ovulation day, since sperm can survive up to ~5 days and the egg about 24 hours.
How accurate is it?
It's a solid estimate for regular cycles. If your cycles vary a lot, ovulation predictor kits or tracking basal body temperature give more precise timing.
Is my data private?
Yes. If you save your result it stays in your own browser on this device — nothing is uploaded. Optional sync and reminders will come with a free account later.