How is ovulation estimated?

Ovulation typically occurs 14 days before the next period. We compute ovulation = LMP + cycle length − 14 days.

What is the fertile window?

Sperm survives up to 5 days and the egg lives ~24 hours, so the fertile window is ~5 days before ovulation through 1 day after.

No. Cycles vary month to month, and ovulation can shift due to stress, illness, travel or medications. Estimates are for planning only.

No — calendar-based fertility tracking is unreliable for preventing pregnancy. Use this for informational purposes only.

Next 6 periods, ovulation dates and fertile windows.

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Follow these steps — everything happens instantly in your browser.

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Step 1. Enter the first day of your last period.
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Step 2. Enter your average cycle length in days.
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Step 3. Enter your typical period length.
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Step 4. Read the next 6 cycles with period start/end, ovulation and fertile window.

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