Calculation
of EDD is not an exact science owing to many uncertainties,
an irregular cycle or uncertainty over date of conception
being common examples. You may notice that your EDD or estimated
date of delivery may differ by a few days from the one your
doctor calculates. This is because doctors calculate in days
since all the months do not have the same number of days.
Most doctors take the first day of your last period or LMP,
add 266 days (38 weeks) plus another 14 days (the average
period for ovulation and conception is 2 weeks after the first
day of the LMP). Early ultrasound offered during the first
three months are considered accurate as babies seem to grow
at a similar rate in the early months
DIY Calculation based on a 28 day cycle:
Take the first day of your LMP e.g. 20th April
Add one year (20th April of the following year)
Subtract 3 months (20th January)
Add 7 days and your EDD will be 27th January
OR
The first day of LMP is April 20, for example.
You add seven days (April 27).
Then add 9 months and you have January 27 as your EDD
Finally the average menstrual cycle
is 28 days so if your cycle is shorter or longer than that
you will need to add or subtract the difference. For example,
if you have a 35 day cycle you will have to add 7 days to
the due date (35 minus 28 equals 7). This will make your due
date February 3rd.
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Once
you know for sure that you are expecting, the first
thing that will come to mind is your due date (if you're
not sure, our Pregnancy Due Date Calculator can help).
Simply enter the first day of your last period
and our Pregnancy due date calculator will not only
calculate your due date and current week but also build
a personalized pregnancy calendar for you.