Ovulation Calculator
Find your likely ovulation day and fertile window for the next few cycles.
About the Ovulation Calculator
Sperm can survive up to 5 days and an egg about 24 hours, so the fertile window is the 5 days before ovulation plus the day of ovulation. Ovulation usually occurs about 14 days before the next period, which is why a longer cycle means later ovulation.
The formula
Ovulation ≈ last period + cycle length − 14 days
Worked example
Example: Likely ovulation = Wed, 1 Apr 2026
- Inputs: First day of your last period: 15 March 2026; Average cycle length: 31 days.
- Formula: Ovulation ≈ last period + cycle length − 14 days
- Result: Likely ovulation = Wed, 1 Apr 2026
Things to keep in mind
- This is an estimate for general information, not medical advice. Talk to a doctor or other qualified professional about your health.
- Not a form of contraception. Ovulation tests or tracking temperature are more precise.
Questions people ask
Can I get pregnant outside the window?
It's unlikely but possible, because ovulation can come earlier or later than expected.
How can I confirm ovulation?
LH urine tests, cervical mucus changes and a rise in basal body temperature all help.