Ovulation Calculator for
Irregular Periods
Standard calculators assume a 28-day cycle. Yours doesn't. Enter your real cycle history and get a personalised fertile window — calculated three different ways.
When did your last period start?
We need this to turn your fertile window into real calendar dates.
This ovulation calculator for irregular periods uses three validated clinical methods — the Ogino-Knaus calendar method, Döring luteal phase back-calculation, and a statistical range method — to estimate your fertile window based on your actual cycle history. Unlike standard ovulation calculators that assume a 28-day cycle, this tool is designed for women with PCOS, irregular cycles, or cycle lengths that vary month to month. All calculations happen on your device. No health data is stored or transmitted.