Estimate your fertile window, ovulation date, and next expected period based on your last period and average cycle length.
Ovulation typically happens a fixed number of days before your next period starts — your luteal phase length — rather than a fixed number of days after your last period. This calculator uses your cycle length and luteal phase to estimate ovulation, then builds a fertile window around it that accounts for how long sperm and the egg each survive.
Sperm can survive in the reproductive tract for up to five days, while a released egg is viable for about 24 hours. That's why the fertile window is shown as the five days before ovulation through one day after — intercourse any time in that range can lead to conception, with the two days before and the day of ovulation giving the highest odds.
Stress, illness, travel, and changes in exercise or weight can all shift ovulation earlier or later than average, even in someone with a normally regular cycle. Tracking basal body temperature or using ovulation predictor kits alongside this estimate gives a more precise picture.
It's a useful starting estimate for people with fairly regular cycles, but actual ovulation can shift by several days cycle to cycle. Ovulation predictor kits, which detect the LH hormone surge, or basal body temperature tracking give more precise real-time confirmation.
The estimate becomes less reliable the more your cycle length varies month to month. If your cycles are consistently irregular, an ovulation predictor kit or a conversation with a healthcare provider will give more reliable guidance.
No. This tool estimates fertile days for those trying to conceive and should not be relied on as a method of contraception, since ovulation timing can vary unpredictably.