Below is a simple, short way on How to Calculate a Pregnant Woman’s due date. This can also serve as your Due Date Calculator. It will help you estimate the date your baby will arrive.

1. Know the first day of your last menstrual period (LMP).

2. Count forward 9 calendar months from that date.

3. Add 7 days & 1 year to the date. That’s your due date!

See examples below;
If your cycle is normal 28 days, your due date or expected date of delivery (EDD) is around 40 completed weeks (i.e. 280 days or 9 months) from the first day you saw blood in your last menstruation (i.e. your last menstrual period, LMP)

If your cycle is longer than 28 days, add the difference between your cycle length & 28 days to your calculated date to compensate. If it’s shorter than 28 days, subtract the difference from your calculated date to compensate.

For example;
If your LMP was 12 June 2020, Count 9 calendar months forward from June (which is March!) Add 7 days & 1 year to the date (which is 12+7=19, and 2020+1=2021, respectively). So your EDD is 19 MARCH, 2021.

However: If you have a 35-day cycle, you need to add 7 days to your Calculated Due Date, i.e. 7 days to 19 March, which is 26TH MARCH, 2021.

If you have a 21-day cycle, subtract 7 days from your Calculated Due date, i.e. 7 days from 19 March, which is 12TH MARCH, 2021.

Note that you can deliver once your pregnancy is “term” i.e. anywhere from 37 to 42 weeks. Most women deliver within this range of time. But people still calculate EDD because most women want a specific date, not a range of time.

NOTE: If the 9 months don’t cross to the next year, you won’t need to add 1 year to your LMP year. E.g. if LMP is January, EDD will be October of the same year. But if LMP is in June, EDD will be in March of the next year.    


Another way:

Calculate your estimated due date using this method, take the first day of your last menstrual period, add seven days to that, and count back three months.
For example, if your last menstrual period started on May 2nd, add 7 days to get May 9th and count back three months to get March 9th.


How do I calculate my due date if I don’t know the date of my last period?

If you don’t know the date of your last period or when you conceived, talk to your provider. They will do an examination, which will likely include a prenatal ultrasound, to determine how far along you are in your pregnancy.

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