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When was your last period?

Please choose the FIRST day your period started.

Average cycle:

How long is your luteal phase?

The number of days between ovulation and your next period.

What’s your height & weight?

Enter your pre-pregnancy weight. People with higher BMIs usually carry longer.

feet   inches

How old are you?

Younger people tend to have longer pregnancies.


What’s your ethnicity?

Caucasians tend to deliver later.

Did you go to college?

People who attended college carry a bit longer. (Weird, right?)

Do you drink alcohol?

People who drink usually carry an extra day.

Do you drink coffee?

People who drink a lot of coffee deliver earlier.


Is this your first pregnancy?

First pregnancies last about 3 extra days longer.

Have you had any bleeding?

Bleeding, especially later, can indicate an earlier delivery.

Please select all that apply

Each of these factors may cause a shorter pregnancy.

Past Pregnancies
Current Pregnancy

More information about the Mittendorf-Williams rule

This study done in 1990 showed that pregnancy lasted an average of 288 days past last menstrual period (LMP) for Caucasian first-time moms. For Caucasian women who were not first-time moms, their date of delivery averaged 283 days past LMP (3 days after Naegele’s rule predicted). This finding is known as the Mittendorf-Williams rule.

Our advanced due date calculator above is based on the Mittendorf-Williams rule.

Whereas our basic due date calculator uses “Naegele’s rule,” which predicts childbirth to occur 280 days after the first day of the last menstrual period. While Naegele’s rule is still the most widely used for calculating pregnancy due dates, the Mittendorf-Williams rule is proving to be more accurate.

Read more about how pregnancy due dates are calculated on our basic due date calculator page.