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About this tool
Estimate cycle dates for education; not reliable contraception.
Important: Calendar-based fertile-window estimates are not a reliable way to determine pregnancy-safe days and should not be relied upon for contraception. Ovulation varies, even with regular cycles.
Understanding menstrual cycle estimates
The estimate assumes ovulation occurs approximately 14 days before the next period. Ovulation can shift, so this calculator cannot identify days when pregnancy is impossible.
Worked example
For a 28-day cycle, the estimated ovulation day is around day 14, but the actual day can vary.
Frequently asked question
Can I use this as contraception?
No. Calendar estimates are not reliable contraception. Discuss effective contraceptive options with a qualified healthcare professional.