What is the fertile window?

The fertile window is the 6 days ending on the day of ovulation — the 5 days before ovulation plus ovulation day itself. Sperm can survive in the reproductive tract for up to 5 days.

How accurate is this calculator?

This is an estimate based on average cycle patterns. Actual ovulation can vary due to stress, illness, or hormonal changes. Ovulation predictor kits (OPKs) give more precise confirmation.

Can I use this to avoid pregnancy?

No. This calculator is for informational purposes only and is not a reliable contraceptive method. Cycles vary and ovulation can shift unexpectedly.

Ovulation Calculator — Find Your Fertile Window

The Ovulation Calculator estimates the day of ovulation and your fertile window based on the first day of your last menstrual period and the length of your cycle. Ovulation typically occurs 14 days before the next period. Your fertile window spans the 5 days before ovulation plus the day of ovulation itself — giving 6 days when conception is possible.

Last Period — Year

Last Period — Month

Last Period — Day

Cycle Length(days)

Frequently Asked Questions

Ovulation typically occurs 14 days before the start of the next period. For a 28-day cycle, this is around day 14. For a 30-day cycle, it would be around day 16.

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