Cycle & Follicular Phase Calculator

See the entered cycle day and an educational follicular, ovulation and luteal phase model.

Your cycle details

Enter your dates to explore your estimated cycle calendar.

Your cycle, at a glance

Calculate to see your dates on a calendar, with clearly marked estimates and cycle details.

Calendar estimates cannot confirm ovulation or identify pregnancy-safe days. Changing your inputs clears the previous calendar.

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About these estimates & sources

Who this is for

Adults tracking natural menstrual cycles. Calendar models describe timing rather than fertility status.

How it works

Cycle day = observation date − actual period start + 1. The ovarian follicular phase runs from the start to the day before modeled ovulation; the luteal model begins the next day. Menstruation overlaps the follicular ovarian phase. No cycle is silently repeated after the next estimated start.

Keep in mind

These are calendar phase labels, not measured hormone levels or instructions for diet, exercise or treatment.
Calendar estimates cannot confirm ovulation or pregnancy and must not be used to label any date pregnancy-safe.
Irregular cycles, hormonal contraception, postpartum changes and perimenopause can make cycle-date predictions unreliable.

Sources

NHS: periods and fertility in the menstrual cycle (opens in a new tab)