Three calculators. Two numbers.
Your last period start and your average cycle length are enough. Everything is calculated in your browser; none of it leaves your device.
- Cycle phase calculatorWork out which of the four cycle phases today falls into, and see how the phases are spread across your current cycle.Open calculator
- Luteal phase calculatorCalculate which cycle day your luteal phase starts on, how many days it lasts and when it ends arithmetically.Open calculator
- Period calendarProject the next period starts from your average cycle length. A plain continuation of your own number, not a prediction.Open calculator
What this calculator is not
These calculators are arithmetic on your own numbers. They are not suitable for contraception, they make no diagnosis and they do not predict ovulation. Cycles vary; a calculated day is not a promise.
Follow your phases day by day in the BodySeasons app
In the app you record how you actually feel and recognise your own patterns across weeks and cycles. No points, no streaks, no grading.