Introducing the Ovulation Calculator — Estimate Your Fertile Window

Educational information only. This tool is not medical advice and not a contraception method. For health or fertility decisions, consult a clinician.

Knowing roughly when ovulation happens helps people trying to conceive — and helps anyone understand their cycle better. The new Ovulation Calculator estimates your fertile window from two simple inputs, entirely in your browser.

What it does

• Fertile window and ovulation day from your last period and cycle length.
• Next expected period and an estimated due date (Naegele’s rule).
• Current cycle day and three upcoming cycles.
• Adjustable luteal phase for cycles that differ from the typical 14 days.

Why it matters — and its limits

A calendar estimate is a useful starting point, but only that: real ovulation shifts month to month, so it can be off by several days. To understand the cycle, the fertile window, and how to combine the estimate with real ovulation signs, read our guide to the fertile window.

Private by design

Reproductive-health data is sensitive, so the Ovulation Calculator deliberately stores nothing — every calculation runs locally and nothing you enter is uploaded or logged. A future privacy-first Pro tier is planned for cycle logging and reminders, but the single estimate stays free.