Period calculator
Predict your next period, ovulation day and fertile window, see them on a calendar, and add them to your phone. Predictions are estimates based on your averages. They are not a method of birth control.
Day one is the first day of full bleeding, not spotting.
Cycle length runs from day one of one period to day one of the next. Most cycles are 21 to 35 days.
Advanced options (optional)
The days between ovulation and your next period. Most people have about 14. Change it only if you know yours.
Calculated in your browser. Your details are not saved or sent anywhere.
Enter the first day of your last period and select Calculate to see your next period, fertile window and calendar here.
Your next period
Calendar
Upcoming cycles
| Period | Ovulation | Fertile window |
|---|
The first row is the period you entered. The margin of error grows the further ahead you look.
Before you rely on these dates
Period and ovulation dates here are estimates calculated from averages. They are not a diagnosis, they cannot confirm that you ovulated, and they should never be used to avoid or guarantee pregnancy.
Cycles that are very short, very long, very painful or very heavy, or that suddenly change, are worth a conversation with a doctor. If you are trying to conceive, a doctor or fertility specialist can help with timing and tests. If you have severe pain, soak through a pad or tampon every hour, or have any urgent symptom, contact your own doctor or emergency services.
