How do ovulation calculators work out your most fertile period?

Fertility calculators help to estimate the day of ovulation and, therefore, the days when you are most likely to get pregnant. However, these types of tools are more accurate when the menstrual cycle is regular.These calculators should not be used as a method of contraception.
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Ovulation Calculator: Track Your Fertile Days

Ovulation calculator – Fertility period, symptoms, best days to get pregnant

Tracking Ovulation, Fertile Window

Calculating Your Monthly Fertility Window

Ovulation and Fertility calculator

Ovulation calculator – Fertility period, symptoms, best days to get pregnant

Ovulation Calculator : Estimate your most fertile days - Clearblue

Ovulation Calculator : Estimate your most fertile days - Clearblue

Tracking your LH surge. Determine your most fertile days using ovulati – PREGMATE

Ovulation Calculator: Estimate your most fertile days

Ovulation calculator: When will I ovulate? - Good To