Fertile Window Calculator

Estimate your fertile window and ovulation date. Not a contraceptive method.

This is an estimate for cycle tracking. It is not a contraceptive method and must not be used to prevent pregnancy.

Fertility Window Calculation

Quickly determine your peak fertility days based on ACOG and ESHRE clinical standards.

Last Period

Enter the first day of your last menstrual period.

Cycle Length

Provide your average cycle length (typically 28 days).

Luteal Phase

Optionally adjust your luteal phase length if you know it.

Common Questions

What is the fertile window?

It is the 6-day interval ending on the day of ovulation when pregnancy is most likely.

When is peak fertility?

Peak fertility occurs on the 2 days before ovulation and the day of ovulation itself.

Related Guides

Go deeper with our evidence-based guides.

View all articles →

How to Know if You Are Ovulating: 6 Signs to Watch

Cervical mucus, LH tests, basal body temperature and more: the signs that suggest ovulation, how reliable each one is and when to see a healthcare professional.

Ovulating Again After Birth Control: Signs to Look For

How to tell ovulation has returned after stopping the pill or other hormonal contraception, how long it can take and when to talk to a healthcare professional.

Basal Body Temperature: How to Measure It and Read Your Chart

Why your basal body temperature rises after ovulation, how to measure it correctly, how to read a biphasic chart and what can throw your readings off.