How to interpret this estimate

Estimate the days around predicted ovulation. Uses an estimated ovulation date about 14 days before the next period.

When this result is useful

Use this calculator to compare how Period start year, Period start month, Period start day, and Average cycle length change Estimated fertile window start, Estimated fertile window end, and Estimated ovulation date, and to review alternative values before using the estimate for planning.

Common limitations

The displayed window spans five days before estimated ovulation through one day after. Cycle-based estimates cannot confirm ovulation and should not be relied on as contraception. Review the units and assumptions before interpreting the result.

This calculator uses the selected inputs and the fixed formula behind the tool to produce an estimate. Review the units, assumptions, and result labels before using the output for planning.

Health results are screening or planning estimates only. They do not diagnose health status or replace advice from doctors, dietitians, or qualified healthcare professionals.

Read the medical disclaimer for more context.