📅 Period Calculator
Predict your next period and fertile window.
How it works
- We take the first day of your last period and your usual cycle length to project the next period.
- Fertile window estimates assume ovulation around mid-cycle for a typical adult menstrual cycle.
- Real cycles vary. Track patterns over a few months for a clearer personal picture.
Common questions
Is this contraception?
No. Do not rely on period or ovulation estimates to prevent pregnancy.
My cycles are irregular - is this useful?
It is less precise. See your GP if cycles are very irregular, painful or change suddenly.
Trying to conceive?
Use alongside our ovulation calculator, and talk to your GP or midwife if you need personalised advice.