Period Tools — Period Calculator

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About

Period Tools is a free period and ovulation calculator. Enter the first day of your last period and your usual cycle length, and it projects your next six cycles, your estimated ovulation day, and the fertile window around it.It is built for the common real-world case where cycles are not textbook 28 days — you set your own cycle and period length, and the projection adjusts rather than assuming an average.Alongside the calculator there are cycle-tracking guides and a printable calendar view. No account, no app to install, and nothing you enter is stored.