Example calculation

Ovulation Calculator for 280 average cycle length

With average cycle length set to 280, review the result alongside the other input values. Adjust one condition at a time to see what changes.

Inputs used in this example

First day of last period2026-01-01

Average cycle length (days)280

Estimated result

Estimated ovulation date

September 24, 2026

Fertile window startsSeptember 19, 2026

Fertile window endsSeptember 24, 2026

The result for ovulation calculator uses the inputs shown above. Change one value at a time to see which assumption makes the biggest difference.

Before using the estimate to make a decision, check whether fees, units, timing, or other real-world conditions fall outside this calculation.

Try a slightly different scenario to see how the result moves — useful for narrowing in on the values closest to your situation.