Health

Ovulation Calculator

Estimate your ovulation day and fertile window based on your last period and average cycle length.

First day of your last period

Average cycle length (days)

Luteal phase length (days)

Usually 12–16 days — this half of your cycle is typically more consistent than the first half.

This is an estimate based on average cycle length, not a measurement of your actual hormones — real ovulation timing varies cycle to cycle, especially with irregular periods. For more precision, consider an ovulation predictor kit, basal body temperature tracking, or cervical mucus monitoring. This tool is not a reliable method of contraception. Everything here is calculated locally in your browser.