What is it?
The Period Calculator predicts when your next periods will start. From the date your last period started and your usual cycle, it shows the days left, how long the period may last and your likely ovulation day.
Who is it for?
Women and girls tracking their cycle, planning travel or events, and noticing irregular cycles early.
How to use it
Enter the First day of your last period, your Cycle length (first day of one period to the first day of the next; 28 if unsure) and how long your Period lasts. The answer appears as you type; there is no Calculate button. Tap Copy result to copy it, or Share on WhatsApp to send it.
Better predictions
- Note your start dates for 3–6 months and use your average cycle length.
- Stress, travel, illness, weight change and some medicines can shift a cycle by several days.
When to see a doctor
Dates are estimates from your average cycle. See a doctor if your cycle is very irregular, shorter than 21 days or longer than 35. Also if periods are very heavy, very painful, last more than 7 days, or stop for 3 months or more without pregnancy. PCOS and thyroid problems are common, treatable causes.
Not contraception
Calendar predictions are not reliable birth control. For the fertile window, see the Ovulation Calculator.
This is general information to help you understand your numbers, not medical advice. Talk to a doctor about your own health.
Open the tool: Period Calculator
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Questions, or an error not listed here?
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