Most pregnancies last around 40 weeks (or 38 weeks from conception), so typically the best way to estimate your due date is to count 40 weeks, or 280 days, from the first day of your last menstrual period (LMP). Another way to do it is to subtract three months from the first day of your last period and add seven days.

How do you calculate 9 months pregnant?

Is pregnancy nine or 10 months long? Your 40 weeks of pregnancy are counted as nine months. But wait … there are four weeks in a month, which would make 40 weeks 10 months.

How many weeks pregnant if due date is?

Your due date is considered to be 40 weeks (280 days) after the first day of your last menstrual period or 38 weeks (266 days) after ovulation. Even if an early ultrasound is used to determine or shift your due date, its still based on the basic idea of a 280-day gestational period.