Cycle planning · Free planning tool

Ovulation & fertile-window estimator

Get a calendar estimate of when ovulation and the days before it may fall. This is a planning aid for regular cycles, not a test of ovulation.

An educational planning aid, not a diagnosis or treatment recommendation.

Your dates, a clearer picture

Use the first day of proper bleeding, not spotting.
Regular cycles only, between 21 and 35 days. See the limitations below before using your result.

Your entries are calculated in this page and are not submitted to ProFertility or saved to your patient record by this tool. Clear the form when using a shared device. These tools provide educational estimates, not medical advice.

How this is calculated

The central estimate uses cycle day = usual cycle length minus 14, counting the first day of bleeding as day 1. The displayed fertile window covers the five days before that estimate and the estimated ovulation day. Real ovulation can be earlier or later.

Before you rely on the result

Use only as a rough guide for regular cycles of 21–35 days. It is unsuitable for irregular or absent periods, postpartum or breastfeeding cycles, hormonal contraception or a medicated fertility cycle. It must not be used to prevent pregnancy. An LH test, clinical history or selected investigations may provide different information.

Sources & further reading

Prepared by ProFertility · Updated 23 October 2026. Questions about your own circumstances? Contact our team.