Ovulation Calculator: The Complete Guide
Estimate your most fertile days. Enter the first day of your last period and your average cycle length to see your estimated ovulation day, your fertile window, and when your next period is due.
Who the Ovulation Calculator is for
People trying to conceive (or avoid conception) who want to estimate their fertile window.
How to use the Ovulation Calculator
- Type your values into the fields above — pick your currency or units where the calculator offers them.
- Results update automatically as you type; there's no submit button and nothing is sent to a server.
- Adjust any input to compare scenarios, then copy the result with a single click.
How it works
Ovulation is estimated about 14 days before the next period: last period + (cycle length − 14). The fertile window spans roughly the five days before ovulation through the day after.
Features
- Estimated ovulation day
- Six-day fertile window
- Next period date
- Adjustable cycle length
Understanding your fertile window
The fertile window is the handful of days each cycle when conception is possible — the five days before ovulation plus ovulation day, because sperm can survive several days. Since ovulation timing varies with cycle length, this calculator estimates it from your cycle. Ovulation tests and body-temperature tracking can confirm the actual day.