Period calculator
Enter the first day of your last period, your cycle length and how long your period lasts. The page lists your next six expected periods and how many days until the next one.
- Next six periods
- Free, no sign-up
This is a standard estimate to plan with. It is general information, and your doctor is the right person for medical advice.
Work out my average cycle from past dates
Runs in your browser. Nothing you type or open is uploaded. Free to use, no account. More everyday tools
How to use it
- Enter the first day of your last period.
- Enter your cycle length and period length, or add past start dates to work out your average.
- Read the next period date and the six coming periods.
Cycle length and predictions
Cycle length is counted from the first day of one period to the first day of the next; the average is about 28 days, and anything from 21 to 35 is common. The page adds your cycle length to your last period to predict the next ones, and shows the expected end date from your period length.
If your cycles vary, paste the start dates of a few past periods and the page uses their average and shows how much they vary, which makes the prediction more realistic. Talk to your doctor if your periods are very irregular, very heavy or stop unexpectedly.
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Questions
How long is a normal cycle?
Between 21 and 35 days is common for adults, with 28 days as the average.
How do I find my average cycle length?
Open Work out my average cycle and paste the start dates of your past periods, one per line. The page calculates the average and the range.
Why was my period early or late?
Stress, illness, travel, weight changes and hormones can all shift a cycle by several days. If it is much later than expected, a pregnancy test or your doctor can help.
Does it predict ovulation?
Use the ovulation calculator for the fertile window and ovulation day.