Ovulation Calculator
Estimate your next ovulation date and fertile window based on your cycle length and last period.
Most people use 14 days unless a provider has told you otherwise.
Enter the first day of your last period to predict your next fertile windows.
Estimated from your cycle length and luteal phase, not from hormone tests, temperature, or cervical mucus tracking. Real cycles vary, so use this as a starting point alongside other fertility signs, especially if you're actively trying to conceive.
How the Ovulation Calculator works
Enter the first day of your last period and your average cycle length, and the calculator projects your estimated ovulation date and fertile window for your next three cycles — useful if you're trying to conceive and want to plan ahead rather than track a single cycle.
You can also adjust the luteal phase length (the days between ovulation and your next period) if you know yours differs from the typical 14-day average, for a more personalized estimate.
Frequently asked questions
How is my fertile window calculated?
Ovulation is estimated by counting back from your next expected period using your luteal phase length (the time between ovulation and your next period, typically 14 days). The fertile window covers the five days before ovulation plus the day of ovulation itself, since sperm can survive in the body for several days.
What's the difference between this and a due date calculator?
A due date calculator works backward from a known pregnancy to estimate a birth date. This tool instead looks forward from your last period to predict upcoming ovulation and fertile windows across your next few cycles — it's built for planning ahead, not for tracking an existing pregnancy.
How accurate is this estimate?
It's a statistical estimate based on average cycle patterns, not a measurement of your actual hormone levels. Real ovulation timing varies cycle to cycle and can be affected by stress, illness, and other factors — ovulation predictor kits or basal body temperature tracking give more precise, cycle-specific results.