Ovulation Calculator – Calculate Your Fertile Days Based on Menstrual Cycle
The ovulation calculator estimates ovulation day and fertile days based on cycle length and last menstrual period start date. Suitable for pregnancy planning.
The tool calculates estimated ovulation day, most fertile window (about 5 days before ovulation and on ovulation day), and estimated start date of next period. The calendar shows the entire cycle visually.
When does ovulation occur?
Ovulation typically occurs 14 days before the next period starts. In a 28-day cycle, it's around day 14. With varying cycle lengths, the ovulation day shifts accordingly — in a 30-day cycle, ovulation is around day 16. The calculator provides estimates — ovulation can vary due to stress, illness, or hormonal factors.
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Browse all tools →The ovulation calculator estimates your most fertile days based on your menstrual cycle. A useful tool for couples planning pregnancy to understand different phases of the cycle.
Enter your last period start date and cycle length, and the calculator estimates your ovulation day and fertile window.
- Estimates ovulation timing based on your cycle length.
- Shows your fertile window (approximately 6 days) in calendar view.
- Track cycles over several months for a more accurate picture.
The estimate is based on average cycle length – actual ovulation day can vary month to month.
- Ovulation typically occurs about 14 days before your next period.
- Irregular cycles significantly reduce the reliability of estimates.
- Ovulation tests and basal body temperature tracking provide more accurate results.
The ovulation calculator is a planning tool, not a contraceptive method or medical device.
- Never use this calculator as contraception – it's not reliable enough for that purpose.
- Consult a doctor if you have fertility concerns.
- Your data isn't stored on our servers – you can use the calculator privately.