Ovulation Calculator
Estimate your fertile window based on the first day of your last period and average cycle length. For family planning; not contraception.
Inputs
Typical: 12-16
Expected ovulation
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Fertile window
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Next period expected
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Estimated due date
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Cycle day of ovulation
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About Ovulation Calculator
How fertile windows work
Sperm can live 3-5 days in the reproductive tract. The egg lives 12-24 hours. So intercourse 1-5 days before ovulation can lead to pregnancy. The 6-day fertile window is your best chance.
Limitations
Cycle length varies. Stress, illness, travel, and many other factors can delay ovulation. Calendar methods alone are unreliable for contraception (10-25% annual failure rate).
Better tracking methods
Basal body temperature, cervical mucus, ovulation predictor kits (LH surge), or fertility monitors give more accurate ovulation timing than calendar math.