Calculator Inputs and Outputs
Inputs
- First day of last period — example: 2026-07-01
- Average cycle length (days) — example: 28
Results
- Estimated ovulation date
- Estimated fertile window
- Estimated next period
Formula used
Estimated ovulation is approximately 14 days before the next expected period. Cycles vary and this is not a contraceptive method.
How to Use the Ovulation Calculator
Enter the requested values, review the units, and select Calculate Ovulation. The result updates immediately using the formula below.
Formula
Estimated ovulation is approximately 14 days before the next expected period. Cycles vary and this is not a contraceptive method.
Example and Accuracy
The default values provide a working example. Change any input to calculate your own result. The calculator keeps full internal precision and rounds displayed values for readability.
Important Note
This calculator provides an informational estimate. Verify critical financial, medical, construction, scientific, or legal decisions with an appropriate qualified professional.
Calculation Standards
This tool uses documented formulas and high-precision internal values. Displayed results may be rounded for readability. Review the assumptions and verify important decisions with a qualified professional.
Read our calculation methodology