Ovulation Calculator

Enter the first day of your last period and your average cycle length to estimate your fertile window, ovulation day, and next expected period.

First day of your last period

Average cycle length (days)

Count from the first day of one period to the first day of the next.

Average period length (days)

Used only to shade period days on the timeline below.

Please select a valid last period date that isn't in the future.

Your estimated cycle

–

Estimated ovulation day

Based on a typical 14-day luteal phase counted back from your next expected period.

–

Fertile window

Most fertile days

This range accounts for sperm survival before ovulation and the egg's short lifespan after it — generally your best window for trying to conceive.

–

Next expected period

Based on your average cycle length. Irregular cycles will shift this date.

–

If conceived this cycle

Estimated due date

Calculated as roughly 38 weeks from your estimated ovulation day — the standard method used when conception timing is known. This only applies if a pregnancy occurs during this cycle's fertile window.

Your cycle at a glance

Period Fertile window Ovulation day Other days ▲ marks today

Good to know This estimate assumes a fairly typical cycle and a standard 14-day luteal phase, which fits many people but not everyone. Cycles can shift month to month due to stress, illness, travel, or other factors, so treat this as a helpful guide rather than a guarantee. If you're tracking ovulation for a specific medical reason, ovulation predictor kits or a discussion with your doctor can add more precision.