Ovulation & Fertile Window Calculator
Estimate your ovulation date and fertile window from your cycle. Free online ovulation calculator.
Frequently asked questions
- How is ovulation estimated?
- By subtracting the luteal phase length, usually 14 days, from your average cycle length and counting from the first day of your last period.
- What is the fertile window?
- The five days before ovulation plus the day after, because sperm survive several days while the egg lives about a day.
- Can I use this for contraception?
- No. Cycle lengths vary and this is only an estimate. Use a reliable method if you want to avoid pregnancy.
- Is my data private?
- Yes, the calculation happens entirely in your browser.
This tool runs entirely in your browser. No data is uploaded anywhere.