How to Calculate a Pregnancy Due Date

Congratulations on your pregnancy! One of the first questions everyone will ask is when the baby is due and you are probably just as interested in this information as they are. Calculating your pregnancy due date is pretty simple and just requires a little knowledge of your own menstrual cycle.

Things You'll Need

• Calendar

Instructions

1. Determine your average menstrual cycle; this is the number of days from the first day of your period until the first day of your next period. For most women this is 28 days. Be sure to notify your obstetrician if you find that you cycle is irregular or tends to be longer or shorter on average.

2. Use a calendar to find the first date of your last menstrual period.

3. Add 7 days to this date.

4. Subtract 3 months.

5. Add or subtract the number of days your period is under or over the 28 day average. If your cycle is 27 days long then subtract one day from your due date, but if your period averages 30 days, add 2 days to your due date.

6. Adjust the year accordingly. Calculate the due date in the following year if the first day of your last period was in March through December. So if your last period started in February, then your pregnancy due date will be the same year, but if your last period started in April, then your due date will be in the following calendar year.

7. Remember that this is the gestational age for your baby and it is calculating your due date based on the day of your last period and not the date of conception.

Tips & Warnings

• You should call your obstetrician immediately after finding out you are pregnant to receive the best prenatal care during your pregnancy.

• A due date is just an estimate of when your baby will be developed enough to survive out of the womb. It also allows for measurements to be made and tests to be given at appropriate times. A baby can be expected anytime from 2 weeks prior to your due date to 2 weeks after your due date.

Resources

• Pregnancy Due Date Calculator