Period Calculator
Estimate upcoming menstrual period start dates.
ResultEstimated next period: August 17, 2026
Following estimates: September 14, 2026; October 12, 2026.
How to use this calculator
- Enter the first day of the latest period and average cycle length.
- Review the live result and use Copy result when you need to share it.
How the calculation works
Each projected start is calculated by adding the average cycle length to the preceding date.
Formula
Each projected start is calculated by adding the average cycle length to the preceding date.
Step-by-step calculation
- Enter the first day of the latest period and average cycle length.
- Each projected start is calculated by adding the average cycle length to the preceding date.
- Check the displayed result, then copy it if needed.
Worked example
With a 28-day cycle, each displayed estimate is 28 days after the previous one.
Risk guidance
Frequently asked questions
Does this tool send my inputs anywhere?
No. The interactive calculation runs in your browser and this site does not submit tool inputs to a backend.
How should I use the result?
Check that the entered units and values match your situation, especially around dates, breaks, and rounding.
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