How to Calculate Pregnancy Due Date

Know when your estimated due date (EDD) is? Your OB-GYN might have told you that’s the date you should note down, yet not many women actually give birth on their EDD. How exactly is your pregnancy delivery day calculated?

How to calculate pregnancy due date

delivery due date baby
EDD is usually calculated with Naegele’s rule. Franz Karl Naegele, the German obstetrician, created the rule based on the assumption that a pregnancy lasts 280 days and the menstrual cycle is 28 days long.

In other words, your EDD can be calculated by adding 280 days (9 months 7 days) to the first day of your last menstrual period. (The first day of the last menstrual period is considered to be Day 1.)

If your cycle is shorter than 28 days, for example, 27 days, you will need to add 9 months 6 days (7 – 1 = 6 days) to get your EDD. If your cycle is longer, you need to add the difference to the 9 months 7 days to get your EDD.

How to use Naegele’s rule

EDD based on Naegele’s rule can be calculated this way:
1. Add 9 months to the month of your last menstrual period
2. Add 7 days to the first day of your last menstrual period

Example: Last menstrual period was on 10th March

3+9=12 (December)
10+7=17 (17th)
∴The EDD is 17th December

If your menstrual cycle lasts for, for example, 30 days, you add 9 months and 9 days (30 – 28 =2, ∴7+2 = 9 days). As a result, you find out your EDD is 19th December.

Every month, week, day and minute counts

couple pregnant woman husband
It’s perfectly normal to not give birth on your EDD – very few women do, actually! However, this EDD at least gives to moms a specific date they can look forward to, or at least start preparing themselves for.

Pregnancy is an unknown territory on which you tread – be it your first, second or third. No one knows when the baby will be delivered; before or after the EDD. Although you have an “expiry date” given to you, don’t be too concerned about it and it’ll be better for you to focus on the fetus’ growth and your own health.

Each day will count as you count down to the very big day in your life, so remind yourself to treasure the present.