Ovulation Calculator
Estimate your ovulation day and fertile window from your last period and cycle length.
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Enter your last period date to estimate your fertile days.
This is a calendar estimate only and not medical advice or a contraceptive method. Real ovulation varies. Consult a healthcare professional for family-planning decisions.
Frequently Asked Questions
When do I ovulate?
Ovulation usually happens about 14 days before your next period starts. The calculator estimates it as your last-period date plus your cycle length, minus a 14-day luteal phase. With a typical 28-day cycle that lands near day 14.
What is the fertile window?
The fertile window is the roughly 6 days ending on ovulation day — the 5 days before plus ovulation itself — because sperm can survive several days. The two days before ovulation are usually the most fertile.
How reliable is this estimate?
It is a calendar estimate based on averages. Real ovulation shifts with cycle variability, stress, and health. For trying to conceive or avoid pregnancy, combine it with ovulation tests or other methods and talk to a healthcare professional.