Ovulation Calculator

Estimate your fertile days from your last period and average cycle length.

Quick answer: Free ovulation calculator: predict your fertile window and next period from cycle length and last period date. Calendar-method estimate.

First day of last period

Average cycle length (days)

–Fertile window

–Estimated ovulation

–Next period ≈

–Ovulation in

Estimate only — not suitable as contraception. Consult a healthcare provider for medical questions.

How to use

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Get your result instantly — nothing is uploaded.

About this tool

The calendar method estimates ovulation about 14 days before the next expected period, with a fertile window of roughly the 5 days before plus ovulation day. Sperm survive up to 5 days, so the window matters more than the single day. Cycles vary month to month — this is an estimate, not contraception guidance.

FAQ

How is ovulation estimated?

Ovulation ≈ next period minus 14 days; the fertile window covers 5 days before through 1 day after.

Is this a reliable contraception method?

No — calendar predictions have real failure rates. Use proven contraception; this tool is for awareness.

My cycles are irregular — will this work?

Irregular cycles make predictions much less reliable. Consider ovulation test kits or medical advice.

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