Ovulation & fertile days calculator

How it works

Enter the first day of your last period and your usual cycle length.

The formula

Ovulation ≈ next period − 14 days. The fertile window is about the 5 days before ovulation plus ovulation day.

Worked example

Period started 1 November with a 28-day cycle: next period around 29 November, ovulation around 15 November, fertile days about 10–15 November.

Good to know

• Cycles vary; this is not a reliable method of contraception.
• Ovulation tests or a doctor give more certainty.