Period Calculator
Enter the first day of your last period and we’ll project your next few cycles — when each period is likely to start, plus your fertile window and ovulation along the way.
Estimates for a regular cycle, for general planning only. Cycles vary — this is not medical advice or contraception.
How it works
Most cycles run 21–35 days, counted from the first day of one period to the first day of the next. From your last period and your usual cycle length, we map out the coming months so you can plan ahead — whether you’re trying to conceive or simply want to know what to expect.
Frequently asked questions
How is my next period predicted? +
We add your average cycle length to the first day of your last period, then repeat that for the following cycles. The more regular your cycles, the more accurate the prediction.
What if my cycles are irregular? +
Predictions assume a fairly regular cycle. If yours vary a lot, treat the dates as a rough guide and consider tracking a few cycles to find your personal average.
Can I use this to avoid or plan pregnancy? +
It can help you understand your fertile window, but calendar estimates alone aren’t reliable contraception. Talk to your provider about a method that fits you.
More tools for this stage
Sibling Age Gap Calculator
Plan the spacing between your kids — pick a gap, get a second due date; or compare two dates.
Open tool →Ovulation Calculator
Pinpoint your fertile window and most likely days to conceive.
Open tool →Pregnancy Test Calculator
Find the earliest day a test can show an accurate result.
Open tool →