Ovulation Calculator

Estimate your fertile window and ovulation day from your last period and cycle length.

First day of last period

Cycle length days

Fill in the fields above and press Calculate or hit Enter ↵

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Fertile window estimates without app friction

Last updated: March 30, 2026

An ovulation calculator estimates likely ovulation and fertile window from cycle timing. Many users want this quickly without account creation or app onboarding.

The method estimates ovulation around 14 days before the next expected period, then marks a fertile window around that date for planning.

This is an educational planning aid and not a medical diagnosis. Cycle variability is normal, so professional guidance is recommended for fertility concerns.

Frequently asked questions

How is ovulation estimated?

Ovulation is typically estimated around 14 days before the next period, based on your average cycle length.

What is the fertile window?

The fertile window usually starts about 5 days before ovulation and ends about 1 day after.

Is this a medical diagnosis?

No. This is an estimate for planning. For medical decisions, consult a qualified healthcare professional.