Next period calculator
Enter your last period, cycle length and period length to plan trips and events and notice any delay.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter first day of your last period, average cycle length, period length (bleeding days) and periods to list.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Start of period n = first day of last period + n × cycle length. End = start + period length - 1.
Example
Inputs: First day of your last period = 2026-09-01, Average cycle length = 30 days, Period length (bleeding days) = 5 days, Periods to list = 6. Result: Next period starts: Thursday, October 1, 2026 (2026-10-01); Next period ends: Monday, October 5, 2026 (2026-10-05).
Limits and caveats
- It assumes every cycle is the same length; real cycles usually vary by a few days.
- Stress, travel, illness and breastfeeding can delay a period.
Questions about this tool
How do I find my cycle length?
Count from the first day of one period to the day before the next one starts, and average it over several months.
What is a normal cycle length?
Between 21 and 35 days for most adults, with bleeding lasting up to 7 days.
When is a late period worth checking?
If it is more than a week later than usual, a pregnancy test or a doctor’s visit may be worthwhile.