The Math behind Baby due date calculator
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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