If you're pregnant, this is an exciting time, eagerly awaiting the arrival of your baby. Gestation is usually 38 weeks, or 266 days from conception to birth. There are several ways to calculate your due date, but you need to know the date you started your last menstrual period, how many days are in your menstrual cycle or when you ovulated. Other ways to determine your due date involve your doctor's help. Remember that your due date is just a guide and that most babies come when they're ready.
Step 1
Count back three months from the start of your last menstrual period. Add seven days. This is called Naegle's Rule and gives you your due date. If your last period started April 1, three months earlier would be Jan. 1. Add one week and your baby's due date is Jan. 7. Or you can add 280 days to the start date of your last period.
Step 2
Measure your basal body temperature. This is an oral temperature taken with a precise digital thermometer upon waking. It's important to take your basal temperature before you get out of bed and start moving. A rise in body temperature can indicate ovulation. Add 266 days to the date of ovulation and that's your due date.
Step 3
Add 266 days to the date of conception. This method only works if you know exactly when you know when your child was conceived.
Step 4
Have an ultrasound performed by your doctor. Your health care provider will be able to determine a due date by the size of the embryo.
Tips and Warnings
- The better you track your ovulation, the more accurate your due date will be. Most calculations assume an average 28 day menstrual cycle with ovulation at day 14. If your cycle is longer or shorter, an ultrasound is the best way to determine your baby's due date.
- Pregnancy due dates are only a guide and less than 5 percent of babies are born on their actual due date. However, 80 percent of babies are born within 10 days of their due date, so think of it as a "due week" instead.
Things You'll Need
- Calendar
- Basal thermometer
- Ultrasound machine
