Ovulation Calculator
Enter your last period date and cycle length to find your fertile window, peak ovulation day, and next period.
Typically 21–35 days
Medical disclaimer
This calculator provides estimates only and is not medical advice. Do not use this tool as a method of contraception. Ovulation timing varies between cycles and individuals. For fertility support or contraceptive guidance, consult a qualified healthcare provider.
How the ovulation calculator works
Ovulation typically occurs about 14 days before your next period, regardless of overall cycle length. If your cycle is 28 days, ovulation is around day 14. If it's 35 days, ovulation is around day 21. Your fertile window is the 5 days before ovulation plus the ovulation day itself — the days when conception is most likely.
Why a single calculator isn't enough
A calculator assumes your cycle is perfectly regular. In reality, cycle length varies month to month — sometimes by several days. Tracking multiple cycles with an app like Dawn Phase lets you see your actual patterns and get more accurate predictions over time.
Note: These are estimates. This tool is not suitable for contraception or fertility treatment decisions.
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