Now that you have confirmed your pregnancy, calculating your due date is likely an important concern. Human gestation takes, on average, about 40 weeks. However, just as with all averages, some pregnancies are longer and some are a bit shorter. Most healthy pregnancies are actually considered full term anywhere between 37 and 42 weeks, but there are several ways to calculate your due date to give you a fairly accurate determination of when to expect your new bundle to arrive.
Step 1
Calculate your due date by the date of your last menstrual period. Determine when the first day of your last menstrual period was, marking this date on a calendar for easy reference. Count up nine months, and then add seven days. This is your due date.
Step 2
Ask your obstetrician or midwife to measure your uterus to determine how far along you are in your pregnancy. From this measurement, you and your doctor should be able to estimate your due date. Using this method in conjunction with the calculations of your last menstrual period will help decrease the margin of error.
Step 3
Have your obstetrician or family doctor perform a blood test. Human chorionic gonadotropin is the name of the hormone that is produced by the placenta. The further along you are in your pregnancy, the more of this hormone will be present in your bloodstream.
Step 4
Consider having an ultrasound performed. This method measures the physical size and development stage of the fetus, so it is the most accurate way to determine your due date, although it is still not an exact date. The very early stages of pregnancy will involve a transvaginal ultrasound, but pregnancies in the later stages will use the more familiar external prenatal ultrasound.
Step 5
Use an online calculator. Multiple online calculators can be found to determine your due date. It is essentially the same as using your last menstrual period, since this is information that must be plugged in to the program, but it does at least reduce the margin of error that is created when counting by hand.
Tips and Warnings
- If you have irregular periods, or you do not keep close track of your menstruation dates, the first and second methods may not be the most reliable methods to determine your due date.
- Few woman actually give birth on their due date, so use this date as a guideline, not an absolute date. To calculate a due date window, add 10 days on either side of this due date, and you will have a large, but relatively accurate, range of dates of when your baby might be born.
Things You'll Need
- Calendar
- Calculator (optional)
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