Find out when your next period is due — and whether it's late — from your last period date and average cycle length.
We take the first day of your last period and add your average cycle length — the number of days from the start of one period to the start of the next. If that predicted date has already passed, we count forward however many cycles it takes to land on the next upcoming date, so you always see a date ahead of today.
If today is past your predicted period date and it hasn't started, this calculator shows how many days late you are based on your average cycle length. A few days' variation is common and not usually a cause for concern; if it's been more than a week, or periods have been irregular for a while, it may be worth checking in with a doctor.
Cycle length is counted from the first day of one period to the first day of the next. Anywhere from about 21 to 35 days is considered typical for adults, with 28 days often used as a default when you haven't tracked your own average.
It'll be less precise the more your cycle length varies, since the calculation assumes a consistent number of days each cycle. Tracking your last 3–6 cycles and using your own average (rather than a guess) will give a noticeably better estimate than a single typical value.