Ovulation Calculator
Estimate fertile window
Ovulation ≈ next LMP − 14 days (luteal phase is constant ~14 d).
- Estimated ovulation
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- Fertile window
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- Next period (predicted)
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Fertile window = 5 days before ovulation through 1 day after. Sperm survive up to 5 days; egg ~24 h.
About this tool
Ovulation Calculator is a single-purpose utility on instant.tw, a free toolbox of calculators, converters, generators, and quick lookups. Everything works in your browser — nothing is uploaded, nothing is stored on a server unless explicitly noted.
Category: Women's Health — Fertility & TTC. Browse more Women's Health — Fertility & TTC tools.