---
title: "Ovulation Calculator — Fertile Window & Ovulation Day"
description: "Calculate your fertile window and ovulation day from your last period and cycle length. References NHS, ACOG, and German BZgA clinical guidance. Free, no ads."
url: "https://worldcalculators.org/calculators/ovulation/"
canonical: "https://worldcalculators.org/calculators/ovulation/"
---

# Ovulation Calculator

Calculate your fertile window and ovulation day from your last period and cycle length. References NHS, ACOG, and German BZgA clinical guidance. Free, no ads.

## Quick answer

Ovulation occurs approximately 14 days before your next period — not necessarily 14 days after your LMP. For a 28-day cycle: ovulation ~day 14. For a 32-day cycle: ~day 18. The fertile window spans 5 days before ovulation to 1 day after (6 days total). This is consistent across NHS, ACOG (US), and BZgA (Germany) clinical guidance.

## Fertile Window by Cycle Length

Days counted from first day of period. Ovulation = cycle length minus 14 days. Fertile window = 5 days before ovulation + ovulation day.

Source: https://worldcalculators.org/calculators/ovulation/
Markdown mirror of the HTML page. Prefer this URL for RAG; the interactive calculator still lives on the HTML page.