How Accurate Is The Calendar Method?

Only as regular as your cycle. Ovulation timing varies month to month even in regular cycles, which is why this method is not reliable as contraception.

Ovulation Calculator

Estimate your ovulation date, fertile window, next period and potential due date from your cycle.

Cycle DetailsCalendar-method estimates you can tune to your own history.

First Day Of Last Period

Cycle LengthdaysLuteal PhasedaysPeriod Lengthdays

Cycles To Project

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What Is the Ovulation Calculator?

The Ovulation Calculator uses the calendar method: ovulation is estimated one luteal-phase length (typically 14 days) before the next expected period, with the fertile window spanning the five days before ovulation through the day after. It also projects the next period and the standard 280-day due date if conception occurs.

How It Works

Enter the first day of your last period, your average cycle length and, if known, your luteal phase length.

When to Use It

Use it to plan conception timing or understand your cycle. Combine it with ovulation test kits or temperature tracking for real confirmation.

Frequently Asked Questions

How Accurate Is The Calendar Method?: Only as regular as your cycle. Ovulation timing varies month to month even in regular cycles, which is why this method is not reliable as contraception.

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