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Ovulation & Fertile-Window Calculator
Estimate your ovulation day, fertile window, and next period from your last period and cycle length.
These are estimates and vary from cycle to cycle — they can't confirm that ovulation has happened and are not a form of contraception. Whatever your reason for tracking, there's no pressure here.
When it can help to seek advice
There's no rush and no judgement — everyone's journey is different. As a general guide, it's worth speaking to your ob-gyn or a fertility specialist if you've been trying to conceive for about 12 months, or 6 months if you're over 35. It's also fine to check in sooner — for example if your periods are irregular or have stopped, or if you have any concerns.
ACOG — Evaluating InfertilityASRM — Reproductive Facts· Last reviewed 20 July 2026
About ovulation & your fertile window
- When am I most fertile?
- Your fertile window is roughly the six days ending around ovulation, because sperm can survive up to about five days and the egg for about a day. Timing intercourse in this window gives the best chance of conceiving.
- How is ovulation estimated?
- We count back about 14 days (the luteal phase, which is fairly constant) from your next expected period: ovulation ≈ your last period start + (cycle length − 14).
- Is this a form of contraception?
- No. These are estimates and vary from cycle to cycle — please don't rely on them to avoid pregnancy. For contraception, speak with a healthcare professional.