How accurate is ultrasound at getting a due date?  picture of
calendar with due dateThere are a few different ways to
calculate a due date. Most often, your due date is calculated by
counting 40 weeks from the first day of your last menstrual
period (LMP).  This is pretty accurate for determining when a
baby is 40 weeks old, which is not the same as when you will go
into labor!! The window for term babies is anywhere from 37 to
42 weeks. Your due date is just the 40 week benchmark. Nobody
can accurately predict the day when you will have your baby, and
only 5% of babies are actually born on their due date.
Calculating a due date is done by counting 40 weeks from the
first day of your last menstrual period (LMP.) Using the LMP is
accurate only if you ovulated and conceived around day 14 of
your cycle. Most women with a 28 day cycle do ovulate around day
14. However, if your cycle is shorter, then you probably ovulate
and can conceive earlier. Likewise, if you have a long cycle
(for example, every 35 days), t