Enter the first day of your last period and your average cycle length to calculate your estimated ovulation date and fertile window. Your results show the 6-day window when pregnancy is most likely, plus your next expected period date — giving you a clear picture of your monthly cycle.
Estimated Ovulation Date
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Fertile Window Start
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Fertile Window End
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Next Expected Period
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Days Until Ovulation
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Ovulation typically occurs about 14 days before your next period starts. This calculator subtracts 14 from your cycle length and counts forward from your last period start date to estimate your ovulation day. For a 28-day cycle, ovulation falls around day 14.
Your fertile window is the roughly 6-day span when pregnancy is possible — the 5 days before ovulation and the day of ovulation itself. Sperm can survive inside the body for up to 5 days, while a released egg is viable for only 12–24 hours, making the days just before ovulation especially important.
No. This calculator is for educational and planning purposes only and should not be used as a form of birth control. Ovulation timing can vary month to month due to stress, illness, and hormonal changes. Speak with your healthcare provider about reliable contraception options.
A regular cycle is one that occurs every 21 to 35 days. If your cycle length varies by more than a few days each month, you have an irregular cycle. This calculator is most accurate for women with regular cycles. Those with irregular periods may benefit from basal body temperature tracking or ovulation test kits.
Common signs include a slight rise in basal body temperature, changes in cervical mucus (it becomes clear and stretchy, similar to raw egg whites), mild one-sided pelvic pain (mittelschmerz), increased libido, and light spotting. Tracking these signs alongside this calculator can improve your accuracy.
Having unprotected sex in the 2–3 days before ovulation and on the day of ovulation gives the highest chance of conception. Maintaining a healthy weight, taking prenatal vitamins with folic acid, reducing alcohol and caffeine, and managing stress can also support fertility.
Stress, illness, travel, extreme exercise, hormonal fluctuations, and breastfeeding can all shift ovulation earlier or later than expected. No calculator can perfectly predict ovulation — it provides an estimate based on average cycle patterns. For greater precision, use ovulation predictor kits (OPKs).
This can happen if you are close to the end of your current cycle and approaching your next period. In that case, enter the first day of your upcoming period (if known) or wait until your next period begins and recalculate for the following cycle.