Ovulation Calculator

First Day of Last Period

Average Cycle Length (days)

How Ovulation Estimation Works

This calculator estimates your ovulation date and fertile window based on your last period date and average cycle length.

The method

Ovulation typically occurs 14 days before your next period. So: Ovulation Date = Last Period Date + Cycle Length − 14.

The fertile window spans approximately 5 days before ovulation through 1 day after, since sperm can survive up to 5 days and the egg lives about 24 hours.

Step-by-step

Enter the first day of your last period.
Enter your average cycle length in days (typically 28, but ranges from 21 to 35 are normal).
The calculator estimates your ovulation date and fertile window.

Worked example

Last period: June 1. Cycle length: 28 days. Ovulation ≈ June 1 + 28 − 14 = June 15. Fertile window ≈ June 10 to June 16.

Important note

This is an estimate based on averages. Actual ovulation varies due to stress, illness, travel, and individual differences. For precise tracking, use ovulation predictor kits or basal body temperature tracking. Consult a healthcare provider for family planning.