Ovulation Calculator
Estimate your next ovulation day, fertile window, and expected next period from the first day of your last period and your average cycle length.
Next period
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Ovulation day
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Fertile window
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How It Works
Ovulation typically occurs about 14 days before the start of your next period. Given your last period start date and average cycle length, the calculator predicts your next period date and counts back 14 days to estimate ovulation.
The fertile window spans approximately 5 days before ovulation plus the day of ovulation itself, since sperm can survive up to 5 days and the egg lives about 24 hours.
These estimates are based on average cycles and are not a guarantee. Cycle length and ovulation timing vary from person to person and cycle to cycle.
Frequently Asked Questions
How accurate is this ovulation estimate?
This tool provides an estimate based on averages. Real ovulation timing can vary by several days even in regular cycles. For precise tracking, use ovulation predictor kits or basal body temperature tracking.
What if my cycle is irregular?
Enter your average cycle length. If your cycles vary significantly, the estimate will be less reliable. Consider consulting a healthcare provider for personalized guidance.
Can I use this to avoid pregnancy?
No. This calculator is for informational purposes only and is not a reliable method of contraception. The fertile window is an estimate, not a guarantee.