Estimate your fertile window and likely ovulation day from your last period and cycle length.
Based on a luteal phase of about 14 days before the next period. Real ovulation varies cycle to cycle; ovulation predictor kits and basal temperature tracking are more precise. Not medical advice.
Ovulation typically happens about 14 days before your next period — so it's counted back from cycle length, not forward from your last period. The fertile window spans the roughly five days before ovulation plus the day itself, because sperm can survive several days.
Ovulation day ≈ cycle length − 14 (counted from the last period)
The luteal phase (ovulation to period) is fairly steady at ~14 days, while the first half varies. Counting back is more reliable than assuming day 14 of every cycle.
It's a calendar estimate. For timing conception more precisely, ovulation predictor kits or basal body temperature tracking pinpoint the day better.
Related: due date calculator · date difference calculator · all free calculators.
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It uses standard formulas and recalculates the moment you change a value, so the math is exact for the inputs you enter. Treat the result as a reliable planning estimate; for decisions with legal or tax consequences, confirm the figures with a qualified professional.
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Last reviewed: September 2026. Free to use, no signup — Ovulation Calculator by ToolWise Digital.
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