Calculate your alternative due date

Due date calculation 2.0

The usual way of calculating your due date is the `Naegele method`. It simply adds 280 days to your last period, or 266 days to your last ovulation date.

The `Mittendorf-Williams method`, shown on this page, takes more factors into account, like race, coffee consumption and education. Some studies have found this to be more accurate than the usual way in calculating due date.

Note: Use this method during the first trimester, and trust your doctor rather than an online calculation

1st day of last period

How to calculate your alternative due date

We add 256.45 days to the first day of your last menstrual period. Next we add or subtract days to this and calculate the total gestational period.


  • A higher BMI results on average in a slightly later due date
  • Non-white mothers have on average a shorter gestation period. (on average 2.5328 days shorter)
  • Higher-educated women are on average 1.1956 days later
  • Drinking alcohol during pregnancy causes a due date which is 1.0463 days later
  • More coffee results in a shorter gestation period. (0.3928 days per cup of coffee)
  • Your first pregnancy lasts on average 3.1169 days longer
  • A weakened cervix may appear around the 18th-22nd pregnancy week. A weakened cervix shortens pregnancy by an average of 18.8054 days
  • Miscarriage is the loss of a baby before the 24th pregnancy week. If you have had one or more miscarriages, your due date may come 0.6990 days earlier
  • A stillbirth is the loss of the baby in or after the 24th pregnancy week. If you have had one or more stillbirths, your due date may come 4.4849 days earlier
  • Bleeding during the first trimester shortens the pregnancy by an average of 2.8788 days

More tools

My due date When is your due date? Enter the date of your last period or ovulation and you'll know. (roughly)

My alternative due date A -according to research- more accurate way to determine your due date.

My fertile days Shows your most fertile days and when you can try a home pregnancy test.

Fetus development This interactive movie shows what pregnancy does to your body!

Calculate your BMI Calculate your BMI. (But not during your pregnancy)