Only one in 20 people give birth on their due date, according to the American College of Obstetricians and Gynecologists (ACOG). But knowing your estimated due date is important, as it’s used to track your baby’s growth and provides a timeline for important tests and diagnostics throughout your pregnancy. You can predict your estimated due date based on simple factors like the first day of your last period.
Pregnancy can come with a lot of unknowns, but your estimated due date doesn’t have to be one of them. Crunch the numbers with our due date calculator to plan for the arrival of your baby.
Due Date Calculator
How to Calculate Your Due Date
Our due date calculator uses the following methods to calculate your due date.
Due Date Based on Your Last Period
This method calculates your due date based on the first day of your last period, assuming a typical pregnancy, on average, lasts 40 weeks (or 280 days) from the first day of your last period. To calculate your due date using this method, you also need to input the average length of your menstrual cycle.
If your menstrual cycle is longer than the average cycle of 28 days, your due date is pushed forward and the amount of time you’re pregnant is reduced. Meanwhile, if your cycle is shorter than the average 28 days, your due date is pushed back.
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Due Date Based on Conception
This method calculates your due date based on the date of conception by assuming a gestation period of 38 weeks (or 266 days) from the date of conception.
Now, Kelly Culwell, M.D., an obstetrician-gynecologist and Forbes Health Advisory Board member, notes that the date of conception isn’t always a reliable method for determining your estimated due date. It’s “often incorrectly estimated due to [the] date of intercourse, which can be several days off from [the] actual date of conception based on the sperm’s ability to survive for five days in the reproductive tract,” she says.
Due Date Based on IVF Transfer
If your pregnancy is the result of a successful in-vitro fertilization (IVF) procedure—in which eggs are extracted and fertilized with sperm, with the resulting embryo later transferred to the uterus—you can calculate your estimated due date based on the timeline of the procedure.
- IVF day 3 transfer: If your embryo was transferred to your uterus after three days of embryo growth, this method calculates your estimated due date based on 263 days from your date of transfer.
- IVF day 5 transfer: If your embryo was transferred to your uterus after five days of embryo growth, this method calculates your estimated due date based on 261 days from your date of transfer.
Due Date by Ultrasound
This method of calculation takes into account the weeks and/or days in which you had an ultrasound. It takes the date of your ultrasound, subtracts the number of weeks at which your ultrasound is done and then adds 280.
Not all the methods described above are the same in terms of accuracy, notes Dr. Culwell. “One of the biggest misconceptions that I see is pregnant people thinking that their due date changes if the dating is slightly different on later ultrasounds, or not believing a due date should change if the first trimester ultrasound is different from what is predicted based on their last menstrual period.”
Instead, she says the most accurate method of calculation (aside from IVF transfer dates, which are the most accurate) is an early first trimester ultrasound and certain date of last menstrual period, followed by the date of conception and lastly, a second or third trimester ultrasound.
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Early Pregnancy Symptoms
It can be difficult to detect pregnancy without a test, as many of the early signs and symptoms mirror those of your period. The most common early signs of pregnancy include:
Less common early symptoms of pregnancy include cramping, spotting (or light vaginal bleeding), food cravings or aversions, headaches and dizziness, fluctuating moods and a metallic-like taste in your mouth.
How Long Can You Go Past Your Due Date?
It is typical for a pregnancy to last between 37 and 42 weeks. A pregnancy lasting beyond 42 weeks is considered post-term, which means the pregnancy is past its due date.
Depending on your health care provider, your pregnancy may reach 41 weeks without any intervention. However, doctors will often run tests on people who are 41 weeks to ensure that the baby is active and healthy. A non-stress test and ultrasound are among the tests a doctor may run on a person who is past 41 weeks pregnant.
Your doctor will look for whether the baby has an adequate amount of amniotic fluid and if the baby is active in the womb. If that is the case, the pregnancy may go on a bit longer until you possibly go into labor on your own. Sometimes, the tests may show the baby is in potential distress, and your doctor may discuss inducing labor.
The risks to both you and your baby increase as a pregnancy reaches 41 to 42 weeks. At this point, your doctor may decide it’s best to induce labor. This is especially true for pregnant people over 40 years old.
Is It Possible for My Due Date to Change?
Typically, an ultrasound is used to confirm your due date (based on your estimated due date calculated from your last menstrual period), and “once a due date has been selected, it does not change no matter how many additional ultrasound exams you may have during your pregnancy,” states ACOG.
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Still, ACOG also notes that “subsequent changes to the EDD (estimated due date) should be reserved for rare circumstances, discussed with the patient and documented clearly in the medical record. A pregnancy without an ultrasound examination that confirms or revises the EDD before 22 0/7 weeks of gestational age should be considered suboptimally dated.”
How Likely Am I to Give Birth on My Due Date?
Though due dates can be helpful to give an estimated time of arrival for expecting parents, they are rarely accurate to the day, according to ACOG.
Factors that can contribute to your baby being overdue—or a postterm pregnancy—are often unknown, but can include:
- If this is your first baby
- If you’re carrying a male fetus
- If you’ve had a previous postterm pregnancy
- If you have obesity
Factors that can lead to preterm birth of your baby (birth before 37 weeks) include:
- Your medical history, such as having a previous preterm baby
- Pregnancy complications, including carrying more than one fetus
- Lifestyle factors, including if you smoke
- If you’re under the age of 17 or over the age of 35
How Accurate Are Due Dates?
No estimated due date is ever 100% accurate, and even ultrasound scans aren’t entirely accurate. However, the ACOG notes that the most accurate method of confirming gestational age is an ultrasound measurement of the fetus or embryo in the first trimester, citing an accuracy of +5-7 days.
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FAQs
How many weeks is a pregnancy?
The majority of pregnancies last between 37 and 42 weeks.
What is an EDD calculator?
An estimated due date (EDD) calculator is a tool to determine your pregnancy’s due date based on the first day of your last menstrual period. As your pregnancy progresses, your doctor can perform ultrasounds that may give a more accurate due date.
How do doctors determine your due date?
If your menstrual cycle was regular before you became pregnant, your doctor will base your estimated due date off the first day of your last period. If your cycles were not regular prior to becoming pregnant, your doctor may use an ultrasound to gauge how far along you are in your pregnancy.
How likely am I to give birth on my due date?
Approximately 60 out of 100 pregnant people give birth on or before their estimated due date[1].
Can you plan a pregnancy due date?
You can try to plan what month your baby may arrive when trying to conceive, but since term pregnancies vary in length from 37 to 42 weeks, it’s unlikely you’ll be able to plan the exact due date.
