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Fertile Days

Which days this month?

Enter the first day of your last period and your cycle length. We give the fertile window, the likely ovulation day and the next period by calendar arithmetic — an estimate, a starting point.

Cycle length is the number of days from the first day of one period to the first day of the next; leave 28 if unsure.

The link carries only the date and the cycle length; nothing is stored on our side.

Source: Wilcox, Dunson & Baird — The timing of the “fertile window” in the menstrual cycle (BMJ, 2000) — the chance of pregnancy concentrates in the five days before ovulation and the day itself.