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Use this ovulation calculator for a clear health & fitness estimate. Results update instantly in your browser.
What this calculator does
Estimate a likely ovulation window from a cycle start date.
How to use this calculator
- Enter the first day of the period and cycle length if available.
- Review the calculation assumptions before using the result.
- The result identifies likely fertile dates.
How to calculate
Ovulation = period start + cycle duration − 14 days; fertile window = ovulation − 7 days to ovulation + 1 day.
Enter the values requested by the ovulation calculator.
Worked example
Use the default values as a worked example, then replace them with your own figures.
Understanding your result
The result identifies likely fertile dates.
- Cycles vary, so do not rely on this alone for contraception.
- Double-check values and units before calculating.
This calculator is educational and is not financial or medical advice.
Frequently asked questions
What does this ovulation calculator do?
Estimate a likely ovulation window from a cycle start date.
How do I use this ovulation calculator?
Enter the first day of the period and cycle length if available.
What does the result mean?
The result identifies likely fertile dates.
What should I check before relying on it?
Cycles vary, so do not rely on this alone for contraception.