Ovulation typically happens about 14 days before your next period starts, regardless of how long your overall cycle runs. This calculator uses that pattern, along with your average cycle length, to estimate your ovulation day, fertile window, and next expected period.
Use this if you're trying to understand your cycle better, whether you're trying to conceive, tracking symptoms, or just want more predictability around your period. If you're actively trying to get pregnant, pairing this with ovulation predictor kits or basal body temperature tracking gives a more complete picture than the calendar estimate alone.
The luteal phase, the time between ovulation and the next period, is fairly consistent at around 14 days, even when overall cycle length varies. This calculator adds your average cycle length to the first day of your last period to estimate your next period, then counts back 14 days from that to estimate ovulation. The fertile window is set from five days before ovulation to one day after, reflecting typical sperm survival time and the egg's short viable window.
Health Calc