How we predict your periods
Each new period is expected one cycle length after the start of the last one. We add your cycle length to the first day of your last period again and again to list your next six periods, and use your period length to show roughly how long each will last. If your last period was a while ago, we roll forward to the next one that is still to come.
Real cycles shift a little from month to month, so treat these dates as a guide. If you are hoping to conceive, the ovulation calculator shows your fertile window too.
