Example calculation

Ovulation Calculator for 28 average cycle length

With average cycle length set to 28, 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)28

Estimated result

Estimated ovulation date

January 15, 2026

Fertile window startsJanuary 10, 2026

Fertile window endsJanuary 15, 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.