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Ovulation Calculator — Free Online (Tolyo.app)

Fertile window prediction by cycle length.

Ovulation Calculator
Updated

Typical cycles range 21–35 days; 28 is common.

Usually ~14 days (defaults to 14).

Likely ovulation
Sat, Apr 25, 2026
Fertile window
Mon, Apr 20, 2026 → Sun, Apr 26, 2026
Next period
Sat, May 09, 2026

Estimates only; cycles vary. For conception or contraception guidance, consult a healthcare professional.

How the Ovulation Calculator Works

This Tolyo.app free online tool estimates ovulation day asLMP + (cycle length − 14 days). Your likely fertile window spans from about 5 days before ovulation through 1 day after.

Key estimates

  • Ovulation ≈ LMP + cycleLength − 14
  • Fertile window ≈ ovulation − 5 → ovulation + 1
  • Next period ≈ LMP + cycleLength

Why Tolyo.app?

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  • Client-side only — your inputs never leave your device.
  • Mobile-first, accessible controls.
  • No login, completely free online.
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Example

LMP = 2025-09-01, cycle length 28 → Ovulation ≈ 2025-09-15, fertile window ≈ 2025-09-10 → 2025-09-16, next period ≈ 2025-09-29.

This Tolyo.app free online calculator provides estimates only and is not medical advice. Consult a healthcare professional for personalized guidance.

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