Ovulation Calculator
Estimate your ovulation day and fertile window for the next cycles.
Enter your values to see the result.
These results are estimates for general information, not medical advice. Body shape, muscle mass, age, ethnicity and health conditions all affect what is right for you, so talk to a doctor or dietitian before making health decisions.
Continue your work
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Clear instructions
Find steps, examples and limitations below.
Use online
Open the tool in a supported web browser.
Free to use
No sign-up required. Tool-specific limits may apply.
How to use the Ovulation Calculator
Estimate your ovulation day and fertile window for the next cycles.
- 1 Enter the first day of your last period.
- 2 Enter your average cycle length and luteal phase.
- 3 Read the next ovulation date, fertile window and upcoming cycles.
Example and practical tips
With a 28-day cycle and 14-day luteal phase, ovulation falls around day 14 and the fertile window runs from about day 9 to day 15.
Frequently asked questions
What is the fertile window?
The five days before ovulation and the day after, when pregnancy is most likely.
Can I use this as contraception?
No. Cycles vary; use ovulation tests or temperature tracking for more accuracy, and proper contraception to avoid pregnancy.
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