Health calculator
Ovulation Calculator for Fertile Window
Estimate ovulation and fertile window dates from cycle length and last period date.
FormulaOvulation date = next period date - 14 days
Formula
Ovulation estimate
Cycle estimates are not contraception, diagnosis, or fertility treatment advice. Consult a qualified clinician for medical guidance.
Ovulation date = next period date - 14 days
For a 28-day cycle, ovulation is estimated around day 14.
FAQ5 common questions for this calculator.
FAQs
Is ovulation always 14 days before the next period?+
No. It is a common estimate and can vary by person and cycle.
How does the Ovulation Calculator calculate the result?+
For the Ovulation Calculator, it uses the Ovulation estimate: Ovulation date = next period date - 14 days. For a 28-day cycle, ovulation is estimated around day 14.
What information do I need to use the Ovulation Calculator?+
For the Ovulation Calculator, enter cycle length and last period date. Keep the units consistent with the calculator fields and compare your setup with the worked example on the page.
How accurate is the Ovulation Calculator?+
Ovulation Calculator is only as accurate as the cycle length and last period date entered. It applies the Ovulation estimate shown on this page, then rounds for readability. Treat the output as screening guidance rather than a diagnosis.
What should I check before using the Ovulation Calculator result?+
For the Ovulation Calculator, check cycle length and last period date, unit choices, and whether the calculator's assumptions fit the person being assessed. Use the result as screening or planning context, not as a diagnosis.
RelatedNearby health calculators for the next step after Ovulation Calculator.
Health guide
How to use the Ovulation Calculator
Estimate ovulation and fertile window dates from cycle length and last period date. The page also explains the ovulation estimate and shows a practical example: For a 28-day cycle, ovulation is estimated around day 14.
- 1
Enter your details
Enter cycle length and last period date, then complete any other fields shown in the calculator.
- 2
Check the calculation
Review the result alongside the ovulation estimate: Ovulation date = next period date - 14 days.
- 3
Compare scenarios
Change one or more inputs to see how they affect the ovulation Calculator result before you use the estimate.