Cycle and ovulation calculators
Cycle and ovulation calculators — 2 tools, each showing the formula it uses, the source that published it, and the date that source was last checked.
Period calculator
A period calculator projects your next period dates from the first day of your last one and your average cycle length. It lists the next six cycles with the fertile window in each, and shows how wide the prediction really is: in 612,613 tracked cycles, only 13 percent were exactly 28 days long.
Ovulation calculator
This ovulation calculator counts back from your next expected period rather than forward from your last one, because the first half of the cycle is what varies. It dates estimated ovulation, ACOG's fertile window of five days before to one day after, and the six-day conception window Wilcox measured in 1995.
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