Fertile window and ovulation calculator
Estimate your fertile window and ovulation day from the last period and cycle length.
Fertile window
06/29 – 07/03
Ovulation day07/02
Next period07/16
Estimate based on a regular cycle. Not a reliable contraceptive method.
How the calculation works
Ovulation happens about 14 days before the next period. The fertile window spans ~3 days before to 1 day after ovulation, when the chance of pregnancy is highest.
Frequently asked questions
Is it a contraceptive method?
Not reliably. Cycles vary and the calendar method often fails.
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Updated on June 17, 2026 · by Rafael Rossi · Methodology & sources