This calculator estimates ovulation and the fertile window for people planning or avoiding pregnancy.
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Enter the first day of the most recent period and the average cycle length. Results are more useful when the average comes from several cycles, especially if the dates tend to wander.
Estimated next period = last period start + average cycle length. Estimated ovulation = estimated next period - 14 days, and the fertile window is approximately the five days before ovulation through one day after.
If a period started August 1 and the average cycle is 30 days, the next period is estimated for August 31 and ovulation for August 17. The estimated fertile window is August 12 through August 18.
No. Fourteen days is a common estimate, but the luteal phase varies between people and sometimes between cycles.
A date estimate alone is not reliable contraception because ovulation can shift. Use an established contraceptive method and speak with a clinician about fertility-awareness methods.
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