How to Find Your Pregnancy Due Date

How to Find Your Pregnancy Due Date

What is the due date?¹

• Your pregnancy due date is the date in the middle of approximately 20 days when your baby is most likely to be born.

• A typical pregnancy lasts about 40 weeks. Most women go into labor on their own within 10 days of their due date, up to 10 days before or after their due date.

• Only a small percentage of babies are born on their due date. Your due date is merely an estimate or educated guess. There is no way to predict when your baby will be born.
   

Why do I require a due date? ¹

• The due date indicates when your pregnancy has reached full term. Being born too soon (before 37 weeks of pregnancy) or too late (after 42 weeks of pregnancy) can put your baby's health at risk.

• This makes it critical for your doctor to keep track of when your baby is due. Your due date also allows your provider to monitor your baby's growth and order testing to check your baby's health at specific points during your pregnancy.

• You can use your expected date of delivery to prepare for your baby's birth and to know what to expect throughout your pregnancy.
   

How does my provider decide my due date?¹

• Your doctor will usually tell you your first due date based on your last menstrual period and the size of your womb at your first visit.

• Conception (when the sperm meets the egg) usually occurs two weeks after your last normal period.

• Most babies are born approximately 40 weeks after your last menstrual period. This means that the time between conception and your due date is approximately 38 weeks.

• Early in pregnancy, most babies grow at the same rate, so the size of your uterus at your first visit can help your provider estimate your due date.
   

Ways to Calculate Your Due Date

Date of Last Menstrual Period^1,2

• Mark down the date when your last period started.
• Add seven days.
• Count back three months.
• Add a whole year.

How accurate is it? Accurate within 2 weeks for women who have regular periods about every 28 days and whose last period was normal.
 

Date of Conception¹

• Using the date of conception, add 266 days.

How accurate is it? Accurate within 1 week or less only if exact day you became pregnant is known, like with infertility treatments 
 

Ultrasound¹

• Ultrasound is used to measure the size of your baby and predict your due date

How accurate is it? Accurate within 1 week or less if done in the first trimester of pregnancy. Accurate within 2 weeks in the second trimester. Accurate within 3 weeks in the third trimester
 

Physical Exam¹

• Findings such as the size of your uterus, presence of a heartbeat, or you feeling your baby’s movement help your provider know how many weeks pregnant you are

How accurate is it? Not very accurate
 

What if my baby doesn’t come on my due date?¹

• Your due date is only an estimate. It is normal for your baby to be born before or after your due date.

• If your baby is born before 38 weeks, he or she may require special care. If you do not go into labor on your own by 41 weeks of pregnancy, your provider may discuss the possibility of inducing labor and/or performing additional testing to ensure your baby's health.
   

What resources are available to help me estimate my due date?²

• Visiting our due date calculator on our website.

• There are many due date calculators available to assist you in estimating your due date. You can use these tools by entering the first day of your last period and then clicking the calculate button.

• These are, once again, only estimates. Speak with your healthcare provider for the most accurate information on your due date.
   

References:

1. When Is My Baby Due?. Journal of Midwifery & Women's Health 2014; 59(6): 672-673.
   Available at: https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmwh.12267.
   Last accessed at: 12.12.2021
    
2. Cleveland Clinic. Calculating Your Estimated Due Date.
   Available at:https://my.clevelandclinic.org/health/articles/10043-calculating-your-estimated-due-date.
   Last accessed at: 12.12.2021