Estimate your fertile window and most likely ovulation day based on your average cycle length.
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If you're trying to conceive, knowing your fertile window makes all the difference. Our free ovulation calculator estimates your most fertile days based on your average cycle length — no app, no sign-up.
In a typical cycle, ovulation happens about 14 days before your next period starts — not 14 days after your last one. That's why cycle length matters: a 28-day cycle and a 35-day cycle have very different ovulation days.
Sperm can survive in the body for up to 5 days, and the egg is viable for about 24 hours after release. That gives you a fertile window of roughly 6 days — the 5 days before ovulation plus ovulation day itself.
Once you have your fertile window, our Pregnancy Due Date Calculator can help once you conceive, and our Calorie & TDEE Calculator in Nutrition helps you plan nutrition alongside your cycle.
It's a solid estimate based on average luteal phase length, but actual ovulation varies by person and cycle. For more precision, combine it with ovulation predictor kits or basal body temperature tracking.
Irregular cycles make calendar-based estimates less reliable. If your cycles vary a lot month to month, talk to your doctor about additional tracking methods.
It's much less likely, but cycles can shift due to stress, illness, or travel, which can shift ovulation timing too.