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Ovulation Calculator
🌸 Ovulation Calculator
Estimate your most fertile days based on the first day of your last period and your typical cycle length, using the standard luteal-phase estimation clinicians rely on.
Ovulation typically occurs about 14 days before the next period starts (the luteal phase length is fairly consistent even when the rest of the cycle varies), so this works backward from your expected next period using your entered cycle length.
Frequently Asked Questions
How accurate is this for irregular cycles?
Less accurate the more irregular your cycle is — this method assumes a fairly consistent luteal phase. Ovulation predictor kits or tracking basal body temperature give more precise real-time confirmation.
Why is the fertile window several days, not just one day?
Sperm can survive in the reproductive tract for up to 5 days, while the egg is viable for about 24 hours after release — so the days leading up to and including ovulation are all potentially fertile.
Can stress or illness shift ovulation timing?
Yes — stress, illness, travel, and significant weight changes can all delay or shift ovulation, which is part of why predictions are estimates rather than guarantees.
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