Ovulation Calculator

Estimate your ovulation day and most fertile window from your cycle.

Estimated ovulation: Thu, Jan 8, 1970

14days after period starts

Fertile window: Sat, Jan 3, 1970 – Fri, Jan 9, 1970

Next period expected (days from last): 28
Fertile window length (days): 7

Estimated ovulation: Thu, Jan 8, 197014

This is an educational estimate, not medical advice. Talk to a healthcare professional about your situation.

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How it works

Ovulation usually happens about 14 days before your next period. Sperm can survive up to 5 days, so the fertile window runs from about 5 days before ovulation to 1 day after.

Formula

Ovulation ≈ Last period + (cycle length − 14) days

Example

With a period starting March 1 and a 28-day cycle, ovulation is around March 15 and the fertile window is March 10–16.

Assumptions & limitations

Results are rounded for display.

Frequently asked questions

Can I use this as birth control?

No. Cycles vary, and calendar estimates are not reliable enough to prevent pregnancy.