What is this calculator?
Estimate the next period and ovulation from a typical cycle length.
What can you use it for?
Use it to understand the numerical relationship between the measurements or dates entered. Estimate the next period and ovulation from a typical cycle length.
How to use it
- Enter first day of last period.
- Enter typical cycle length (days).
- Select Calculate (or Generate for random tools).
- Read the answer and any additional results below the form. Check the units and the limits of the method.
Formula and method
Estimated ovulation = last period + cycle length − 14 days
The model assumes a constant cycle and an approximately fourteen-day luteal phase.
Worked example
First day of last period: 2026-10-08, Typical cycle length (days): 28. The result is 5 November 2026 (estimated next period).
Assumptions and limits
Calendar estimate only, especially uncertain for irregular cycles. Not contraception or a fertility diagnosis.
Frequently asked questions
What inputs does the Ovulation Calculator need?
Use first day of last period, typical cycle length (days). Read the answer and any additional results below the form. Check the units and the limits of the method.
What assumptions apply to the Ovulation Calculator?
Calendar estimate only, especially uncertain for irregular cycles. Not contraception or a fertility diagnosis.