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Use this period calculator for a clear health & fitness estimate. Results update instantly in your browser.
What this calculator does
Predict a likely next period date from the last period and cycle length.
How to use this calculator
- Enter the start date and typical cycle length.
- Review the calculation assumptions before using the result.
- Use the result for calendar planning.
How to calculate
Next period = last period start + cycle duration; period end = next start + period duration − 1 day.
Enter the values requested by the period calculator.
Worked example
Use the default values as a worked example, then replace them with your own figures.
Understanding your result
Use the result for calendar planning.
- Irregular cycles reduce prediction accuracy.
- Double-check values and units before calculating.
This calculator is educational and is not financial or medical advice.
Frequently asked questions
What does this period calculator do?
Predict a likely next period date from the last period and cycle length.
How do I use this period calculator?
Enter the start date and typical cycle length.
What does the result mean?
Use the result for calendar planning.
What should I check before relying on it?
Irregular cycles reduce prediction accuracy.