Ovulation Calculator: Fertile Window and Next Period Dates
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From the first day of one period to the first day of the next.
These are estimates from the calendar method, which assumes ovulation about 14 days before your next period. Real cycles vary month to month, so do not rely on this calculator to avoid pregnancy. Ovulation test kits, tracking temperature, or a doctor can give a more accurate picture.
Next fertile window
12 to 17 October 2026
- Ovulation (estimate)
- 17 Oct
- Next period due
- Sat, 31 Oct 2026
- Period expected until
- 4 Nov
- Pregnancy test from
- 31 Oct
Most home pregnancy tests work from the first day of a missed period.
October 2026
November 2026
- Period
- Fertile window
- Ovulation
- Today
Your next three cycles
- Cycle 1Fertile window12 to 17 October 2026Ovulation (estimate)Sat, 17 Oct 2026Next period dueSat, 31 Oct 2026
- Cycle 2Fertile window9 to 14 November 2026Ovulation (estimate)Sat, 14 Nov 2026Next period dueSat, 28 Nov 2026
- Cycle 3Fertile window7 to 12 December 2026Ovulation (estimate)Sat, 12 Dec 2026Next period dueSat, 26 Dec 2026
How this works
Each period is predicted by adding your average cycle length to the first day of the last one. Ovulation is estimated as 14 days before the next period, because the second half of the cycle (the luteal phase) is usually fairly constant, while the first half varies more. For a 28-day cycle that is about 14 days after your period starts.
The fertile window is the 5 days before ovulation plus ovulation day itself, 6 days in all, because sperm can survive for several days while an egg lasts about a day. The chance of conceiving is highest in the 3 days ending on ovulation day.
This is the calendar method, an estimate only. Cycles of 21 to 35 days are normal, but ovulation can shift from month to month, especially with irregular cycles, after stopping hormonal contraception or while breastfeeding. Do not use it as contraception. Ovulation test kits, temperature charting or a GP or gynaecologist can give a more accurate picture.
FAQs
When do I ovulate on a 28-day cycle?
Around 14 days after your period starts, which is 14 days before the next one. If your last period started on 1 October, ovulation is around 15 October and your fertile window is about 10 to 15 October.
How long is the fertile window?
About 6 days: the 5 days before ovulation and ovulation day itself. Sperm can survive in the body for up to 7 days, so sex a few days before ovulation can still lead to pregnancy.
When do I ovulate on a 32-day cycle?
About 18 days after your period starts (32 minus 14). If your last period began on 1 October, ovulation is around 19 October, the fertile window about 14 to 19 October and your next period is due on 2 November.
When should I take a pregnancy test?
Most home pregnancy tests can be used from the first day of a missed period. On a 28-day cycle starting 1 October, that is 29 October.