Period calculator for teens
A soft guess for the next period — a window for the school bag, not a promise that it lands on one Tuesday.
How this estimate works
Count forward from the first day of bleeding. Once a cycle has settled, many people see the next period about every21 to 35 days. In the first year or two after a first period, doctors expect a much wider spread: the next one often shows up somewhere between 21 and 45 days, and a skipped month is common. That is why the default here is a range. A single date is a guess you can pack around.
More on why early cycles jump around: irregular periods in the first years.
Questions people ask
How do you calculate the next period?
Take the first day of the last period and add the usual gap. If periods are still new, use a window of about 21 to 45 days instead of one number.
What if the window already passed?
A late period in the early years is ordinary. When the next one starts, use that new date. If periods stop for several months after they had been steady, or if anything feels scary, check in with a trusted adult and a doctor. Thewhen to ask a doctor list is short and specific.
General information for families, not medical advice. For a health worry, talk with a trusted adult and a doctor.