RapidCheck

Ovulation Calculator

Estimate your ovulation day and fertile window.

Last updated: 21 Aug 2026

Quick answer

Ovulation is estimated about 14 days before your next period: ovulation ≈ LMP + (cycle length − 14). The fertile window is roughly the 5 days before ovulation plus the ovulation day. Enter your LMP and cycle length above. This is an estimate, not a contraceptive method.

Estimate your ovulation day and fertile window from your last period and average cycle length. Ovulation is about 14 days before the next period; the fertile window spans the ~5 days before it plus the ovulation day.

How to calculate your ovulation day

  1. 1 Enter the first day of your last period.
  2. 2 Enter your average cycle length (default 28 days).
  3. 3 We estimate ovulation and your fertile window.

Frequently asked questions

When do I ovulate?
Typically about 14 days before your next period, so roughly LMP + (cycle length − 14).
What is the fertile window?
The ~6 days ending on ovulation day — the days you are most likely to conceive.
Is this reliable for contraception?
No — it is an estimate for planning conception, not a birth-control method.

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