How to use the Ovulation Calculator
- Enter the first day of your last period.
- Enter your average cycle length (and luteal phase if you know it).
- See your fertile window and the dates for the next cycles.
How it is estimated
Ovulation usually happens about 14 days before the next period (the luteal phase), so in a 28-day cycle it falls around day 14. Sperm can survive up to five days, so the fertile window is the five days before ovulation plus the day itself.
This is an estimate based on averages and is not a method of contraception. Ovulation tests or tracking basal body temperature give more personal timing. Planning ahead? See the Due Date Calculator.
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Tools that pair well with the Ovulation Calculator
- Date Calculator — Find the date that is a number of days, weeks, months or years before or after another date — with an option to count business days only.
- Calorie Calculator — Estimate how many calories you burn per day — your BMR at rest and TDEE with activity — and the daily calories to lose, maintain or gain weight.
- Water Intake Calculator — Estimate how much water to drink each day from your weight, how active you are and how hot it is — shown in liters, ounces and glasses.
- Age Calculator — Enter a date of birth to get the exact age in years, months and days — plus total days and weeks lived, the weekday you were born on, a countdown to the next birthday and your star sign.
Frequently asked questions
How accurate is an ovulation calculator?
It works best for regular cycles. Cycle length varies, so ovulation can shift by several days.
Can I use this to avoid pregnancy?
No. Calendar estimates are not reliable contraception.
Is anything I enter saved or sent?
No. The calculation runs in your browser. Your last inputs are remembered on this device only, so the page opens where you left off.
Can I install Ovulation Calculator as a web app and use it offline?
Yes. Ovulation Calculator is an installable web app (PWA) — installed from your browser, not downloaded from an app store. Click Install app at the top of this page in Chrome or Edge (Windows, macOS, Linux, ChromeOS) or on Android, use Share → Add to Home Screen on iPhone and iPad, or File → Add to Dock in Safari 17+ on a Mac. It then opens in its own window with its own icon, and because it runs entirely in your browser it keeps working offline. Firefox on desktop can’t install web apps. How installing works.