Period Calculator
Estimate your next period, expected bleeding days, planning window, and future cycle dates from one average or several recent cycles.
Your cycle information
Enter 2–12 cycle lengths separated by commas.
Your estimate
Estimated next period
—
—
How the period forecast works
The calculator adds the average cycle length to the first day of your last period. When you enter several recent cycles, it uses their rounded average and displays an earliest-to-latest planning range based on the shortest and longest entries.
Track patterns, not only dates
Recording period starts, bleeding duration, flow, pain, spotting, and symptoms can help you recognize changes and provide useful information to a healthcare professional. Calendar forecasts cannot identify the cause of irregular, painful, heavy, or missed periods.
Frequently asked questions
What counts as cycle day 1?
Cycle day 1 is the first day of menstrual bleeding. The cycle ends the day before the next period begins.
What if my cycles vary?
Use the recent-cycle option. A wider shortest-to-longest range means future dates are less predictable.
Can this confirm pregnancy?
No. A late or missed period has many possible causes. Use an appropriate pregnancy test and seek medical advice when needed.
Can this replace contraception?
No. Do not use a calendar prediction alone to prevent pregnancy.
Medical notice
This calculator provides educational date estimates only. Seek medical advice for very heavy bleeding, severe pain, bleeding between periods or after sex, pregnancy concerns, or a significant change in your usual pattern.
Related calculators