How to Calculate a Due Date During the First and Second Trimester

When you're pregnant, finding the accurate due date of the baby is important so your obstetrician or midwife can monitor the growth of the baby accurately. The most important thing you can do is get early prenatal care. The first appointment with a doctor or midwife usually occurs around 12 weeks. At this point, at the end of the first trimester and through the second trimester, your due date will be confirmed.

Things You'll Need

• Physician or midwife

Show More

Instructions

How to Calculate Your Due Date

• 1

  Determine the first day of your last period before you got pregnant. This is the date your doctor or midwife will use to figure out your due date. Remember that spotting does not count as part of a period, so if you typically spot before or after your period, don't count those days.

• 2

  Count out the days on a calendar to calculate your due date. A pregnancy is approximately 266 days from conception or about 280 days from the date of your last menstrual period. By counting 280 days from the first day of your last period, you should be able to estimate your due date.

• 3

  Visit your doctor or midwife and have her confirm your due date by checking the size of your uterus. She can do this by simply pressing on your abdomen, feeling the uterus and measuring it. She will see if her calculations on how big your uterus should be match with the due date you've figured out based on your last period.

• 4

  Make an appointment for an ultrasound for an accurate due date estimation. You can usually do this early in your second trimester. An ultrasound can provide detailed measurements of both the baby and your uterus. Drink 32 ounces of water approximately one hour before your appointment. A full bladder allows for a better picture of the baby and more accurate measurements.