How to Calculate Estimated Due Date



Once you are pregnant you can’t wait to know when to expect your baby bundle of joy! Newly expecting parents look forward to finding out their EDD, expected due date, and often times like to try and figure out what that date might be before they visit the doctor. Sometimes, too, the EDD can help support or contradict the EDD that is based on the baby’s first ultrasound.


Calculating EDD

In order to calculate your EDD you must know the first day of your last period. Keep in mind, too, that the calculations used are based on women with a 28 day cycle. If you have a shorter or longer cycle then you should keep track of that as it will affect your baby’s due date. The following formulas are quite commonly used to determine an estimated due date and both will give you the due date of your baby!

First day of your last period + 7 days – 3 months = due date

For example, if the first day of your last period was March 3 then your due date would be December 11, give or take a day or two!

First day of your last period + 281 days = due date





So, if the first day of your last menstrual period is March 3 then you add 281 days to that and the end day is your due date! You can count up 281 days on the calendar from the first day of your last period to get the result.

Of course, if math isn’t your strong suit or you simply prefer for someone else to do all the work then consider using a due date calculator on the web. You include the first day of your last period, your average cycle length, and luteal phase, and your estimated due date will be provided to you!

If you know the date you conceived and are 100% positive then all you need to do is add the days of an average pregnancy to the date of conception. That is 267 days or 38 weeks.

Remember, though, that estimated due dates are just that, estimates. They can’t tell you when your baby will be born. Instead, they give you an estimate as when to expect your little one!


Last modified: February 10, 2013

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