Exactly How Accurate Are Due Dates?

 Joline Buscemi Profile Photo
By Joline Buscemi | Updated on Feb 5, 2024
Image for article Exactly How Accurate Are Due Dates?

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Finding out your due date is one of the first little pleasures of pregnancy. Not only is it a marker for your little one’s arrival earthside, it’s also one of the only things you know about your baby—and friends, relatives, and strangers alike are sure to ask about it. But don’t start diving into their astrology birth chart yet. The likelihood of actually giving birth on that day is actually pretty slim.

“Only about 5 percent of all babies are born on their due date,” explains Christy Evans, board-certified OB-GYN at Almond. The majority of babies—90 percent of them—are born within two weeks of their due date. “A normal duration of pregnancy is anywhere between 37 and 42 weeks, so there's a wide range of normal!” says Dr. Evans.

If delivering your baby on their due date is so rare, why have a date at all? Instead of thinking of your due date as an exact arrival time, Dr. Evans says it’s better to look at it as a guide for monitoring your pregnancy’s progression and keeping track of the growth of the fetus. 

Even so, you’re probably curious to know your chances of delivering early, late, or right on time. 

Why Do Due Dates Get It So Wrong? 

Knowing that your due date is likely not going to be your baby’s birthday is one thing, but watching that date come and go can still drum up some disappointment. If that’s you, you’re not alone. Keep in mind that almost 60 percent of births1  occur between 39 and 41 weeks, with 26 percent during weeks 37 and 38. Only around 7 percent of births happen at 41 weeks or more. These stats include inductions, too, which make up around 32 percent of births in the United States. While the exact timing of these inductions vary, research like the ARRIVE study2  encourages inductions at 39 weeks, and they are often suggested for those who are past their due date. 

Regardless, the time spent waiting can be difficult emotionally. “In the beginning of my pregnancy, I wasn’t concerned about going beyond my due date, because I know many first-time moms do,” shares Shalina Seifert, who went four days past her due date. “Unfortunately, I had a very hard pregnancy, and towards the end I became very uncomfortable. I was not able to sit or walk, and essentially spent the last few weeks in bed. Even though logically I knew going over my due date was likely, I was so frustrated.” 

There are many factors that contribute to this wide range in due date vs. birth date, but one reason might be that your due date is inaccurate because of how it was calculated. “The most accurate way to determine the due date is by an ultrasound completed between 11 and 14 gestational weeks. Even if you carefully track your ovulation and know when your baby was conceived, your due date is still an estimate, because every pregnancy is different,” says Dr. Evans. While an early ultrasound can more accurately estimate your due date, those calculated solely from the last missed period rather than ovulation date are even more prone to error. This is especially true for people who have long or irregular cycles. In fact, one study3  found that using the last missed period to calculate the due date resulted in more women going past their projected  date.

What Actually Causes Women to Go Into Labor? 

Surprisingly, experts still aren’t certain what triggers a woman to go into labor (the leading theory4  is that the baby releases a signal to the mother’s body when they are finished developing and ready for the outside world), but barring induction techniques, when labor occurs is largely outside of anyone’s control (so you can put down the hot sauce). Instead, it’s helpful to look at what the science tells us for clues about when the big day might arrive.

Late arrivals

Studies have found several factors that can lead to a longer pregnancy and delivering past your due date. Higher BMI, first pregnancies, having a boy, and having a mother who went past her due date have all been studied5  as potential factors for your bundle of joy making you wait a bit longer. Advanced maternal age6 , defined as those 35 and older, is also a risk factor for late delivery, but induction prior to 40 weeks is often recommended to reduce complications.

And while you might have heard that second babies come faster, Dr. Evans explains this may not be true. “It tends not to change in actuality! Often, if your first baby came after your due date, you're more likely to have any subsequent babies after their due dates as well,” she says.

Early births

On the other hand, too-early births, usually defined as before 37 weeks, can mean a NICU visit. About 10 percent of births are considered preterm, with very early preterm (less than 34 weeks) hovering around 3 percent. “The most common causes of preterm deliveries are chronic health conditions, such as diabetes, drug or alcohol abuse, multiple pregnancies, such as twins or triplets, preeclampsia, or problems with the uterus or cervix,” says Dr. Evans. In some of these cases, your body may spontaneously go into labor early, or your healthcare provider may recommend an induction for the health of you or your baby.

Labor-inducing tricks

Unfortunately for parents who want to meet their baby ASAP—or plan their hospital stay for a lazy Sunday—at-home labor-inducing tricks aren’t a guarantee. Sex, spicy food, teas, exercise, and more are often recommended, although the evidence for these is more anecdotal than supported by studies. So, if you want to have a quick romp to see if it gets things moving, go ahead! Just don’t go in with any expectations besides having a little fun. 

In-office procedures, like a membrane sweep in which your provider uses a gloved finger to separate the amniotic sac from the uterus, are said to induce labor in 1 in 8 woman, although some people argue that labor would have begun regardless of whether a membrane sweep was performed or not (and the same can be said about at-home methods). In short, don’t worry, you’ll most likely go into labor when your body is ready. 

Can You Predict When You Might Go Into Labor?

If you’re reading this in anticipation of your own delivery day, you might be looking for signs that the time is near. But having symptoms—or even the lack of—doesn’t necessarily mean labor is starting soon. “Sometimes—not always—you may have signs that your body is preparing for labor,” says Dr. Evans. 

“You might notice a change in the discharge from your vagina or a few cramps in your abdomen. You may have a low, dull ache in your back that can come and go. You may also feel pressure in your vagina,” she explains. Even dilation isn’t a sure thing. While your doctor may perform a cervical check several weeks before your due date, not even dilation can predict how soon labor will begin.

It can be frustrating, but often the only way to know that delivery day is around the corner is once contractions begin with consistency, or your water breaks. Until then, think of your due date as a guide rather than a guaranteed ending. And while it might feel like you’re enduring a never-ending pregnancy, it definitely won’t last forever. 

So, How Do You Deal?

While patience might be in short supply, when waiting to go into labor it’s best to take each day as it comes. “I think when you’re struggling you have an ‘end date’ in mind and when that date comes and goes, it’s so hard. It’s probably best to set the ‘end date’ in your mind as 41 weeks (as opposed to 40 weeks) to avoid disappointment,” suggests Seifert. 

“My advice is to treat yourself every day that you go past. Every day that I went past my due date, I treated myself to something fantastic. A special lunch, a new pair of pajamas, anything!” says Seifert. However difficult it might be to watch the days tick by with no sign of labor, try to enjoy these pre-baby days, because they are definitely numbered. When the baby does arrive—even if it feels long overdue—all that waiting will finally feel worth it.

Pregnant woman holding her stomach on a bed with a plant in the background

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Your privacy is important to us. By subscribing you agree to our Privacy Policy and Terms & Conditions.

Expectful uses only high-quality sources, including academic research institutions, medical associations, and subject matter experts.

  1. CDC"National Vital Statistics Reports ", vol. 67, no. 8Nov 7, 2018https://www.cdc.gov/nchs/data/nvsr/nvsr67/nvsr67_08-508.pdf.

  2. William A. Grobman, M.D., Madeline M. Rice, Ph.D., Uma M. Reddy, M.D., M.P.H., Alan T.N. Tita, M.D., Ph.D., Robert M. Silver, M.D., Gail Mallett, R.N., M.S., C.C.R.C., Kim Hill, R.N., B.S.N., Elizabeth A. Thom, Ph.D., Yasser Y. El-Sayed, M.D., Annette Perez-Delboy, M.D., Dwight J. Rouse, M.D., George R. Saade, M.D."Labor Induction versus Expectant Management in Low-Risk Nulliparous Women"The New England Journal of Medicine, vol. 379Aug 9, 2018, pp. 513-523https://www.nejm.org/doi/full/10.1056/nejmoa1800566.

  3. David A Savitz, James W Terry Jr, Nancy Dole, John M Thorp Jr, Anna Maria Siega-Riz, Amy H Herring"Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination"American Journal of Obstetric Gynocology, vol. 187, no. 6Dec 1, 2002, pp. 1660-6https://pubmed.ncbi.nlm.nih.gov/12501080/.

  4. Debby Amis, RN, BSN, CD(DONA), LCCE, FACCE"Healthy Birth Practice #1: Let Labor Begin on Its Own"The Journal of Perinatal Education, vol. 23, no. 4Oct 1, 2014, pp. 178–187https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4235056/#:~:text=Many%20scientists%20now%20believe%20that,%2C%20%26%20Mendelson%2C%202004)..

  5. Rebecca Dekker, PhD, RN" The Evidence on: Due Dates"Evidence Based Birthhttps://evidencebasedbirth.com/evidence-on-due-dates/.

  6. "Pregnancy at Age 35 Years or Older"ACOG, vol. 11Aug 1, 2022https://www.acog.org/clinical/clinical-guidance/obstetric-care-consensus/articles/2022/08/pregnancy-at-age-35-years-or-older#:~:text=We%20recommend%20proceeding%20with%20delivery,stillbirth%20beyond%20this%20gestational%20age..


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Updated on Feb 5, 2024

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Exactly How Accurate Are Due Dates?

 Joline Buscemi Profile Photo
By Joline Buscemi | Updated on Feb 5, 2024
Image for article Exactly How Accurate Are Due Dates?

Finding out your due date is one of the first little pleasures of pregnancy. Not only is it a marker for your little one’s arrival earthside, it’s also one of the only things you know about your baby—and friends, relatives, and strangers alike are sure to ask about it. But don’t start diving into their astrology birth chart yet. The likelihood of actually giving birth on that day is actually pretty slim.

“Only about 5 percent of all babies are born on their due date,” explains Christy Evans, board-certified OB-GYN at Almond. The majority of babies—90 percent of them—are born within two weeks of their due date. “A normal duration of pregnancy is anywhere between 37 and 42 weeks, so there's a wide range of normal!” says Dr. Evans.

If delivering your baby on their due date is so rare, why have a date at all? Instead of thinking of your due date as an exact arrival time, Dr. Evans says it’s better to look at it as a guide for monitoring your pregnancy’s progression and keeping track of the growth of the fetus. 

Even so, you’re probably curious to know your chances of delivering early, late, or right on time. 

Why Do Due Dates Get It So Wrong? 

Knowing that your due date is likely not going to be your baby’s birthday is one thing, but watching that date come and go can still drum up some disappointment. If that’s you, you’re not alone. Keep in mind that almost 60 percent of births1  occur between 39 and 41 weeks, with 26 percent during weeks 37 and 38. Only around 7 percent of births happen at 41 weeks or more. These stats include inductions, too, which make up around 32 percent of births in the United States. While the exact timing of these inductions vary, research like the ARRIVE study2  encourages inductions at 39 weeks, and they are often suggested for those who are past their due date. 

Regardless, the time spent waiting can be difficult emotionally. “In the beginning of my pregnancy, I wasn’t concerned about going beyond my due date, because I know many first-time moms do,” shares Shalina Seifert, who went four days past her due date. “Unfortunately, I had a very hard pregnancy, and towards the end I became very uncomfortable. I was not able to sit or walk, and essentially spent the last few weeks in bed. Even though logically I knew going over my due date was likely, I was so frustrated.” 

There are many factors that contribute to this wide range in due date vs. birth date, but one reason might be that your due date is inaccurate because of how it was calculated. “The most accurate way to determine the due date is by an ultrasound completed between 11 and 14 gestational weeks. Even if you carefully track your ovulation and know when your baby was conceived, your due date is still an estimate, because every pregnancy is different,” says Dr. Evans. While an early ultrasound can more accurately estimate your due date, those calculated solely from the last missed period rather than ovulation date are even more prone to error. This is especially true for people who have long or irregular cycles. In fact, one study3  found that using the last missed period to calculate the due date resulted in more women going past their projected  date.

What Actually Causes Women to Go Into Labor? 

Surprisingly, experts still aren’t certain what triggers a woman to go into labor (the leading theory4  is that the baby releases a signal to the mother’s body when they are finished developing and ready for the outside world), but barring induction techniques, when labor occurs is largely outside of anyone’s control (so you can put down the hot sauce). Instead, it’s helpful to look at what the science tells us for clues about when the big day might arrive.

Late arrivals

Studies have found several factors that can lead to a longer pregnancy and delivering past your due date. Higher BMI, first pregnancies, having a boy, and having a mother who went past her due date have all been studied5  as potential factors for your bundle of joy making you wait a bit longer. Advanced maternal age6 , defined as those 35 and older, is also a risk factor for late delivery, but induction prior to 40 weeks is often recommended to reduce complications.

And while you might have heard that second babies come faster, Dr. Evans explains this may not be true. “It tends not to change in actuality! Often, if your first baby came after your due date, you're more likely to have any subsequent babies after their due dates as well,” she says.

Early births

On the other hand, too-early births, usually defined as before 37 weeks, can mean a NICU visit. About 10 percent of births are considered preterm, with very early preterm (less than 34 weeks) hovering around 3 percent. “The most common causes of preterm deliveries are chronic health conditions, such as diabetes, drug or alcohol abuse, multiple pregnancies, such as twins or triplets, preeclampsia, or problems with the uterus or cervix,” says Dr. Evans. In some of these cases, your body may spontaneously go into labor early, or your healthcare provider may recommend an induction for the health of you or your baby.

Labor-inducing tricks

Unfortunately for parents who want to meet their baby ASAP—or plan their hospital stay for a lazy Sunday—at-home labor-inducing tricks aren’t a guarantee. Sex, spicy food, teas, exercise, and more are often recommended, although the evidence for these is more anecdotal than supported by studies. So, if you want to have a quick romp to see if it gets things moving, go ahead! Just don’t go in with any expectations besides having a little fun. 

In-office procedures, like a membrane sweep in which your provider uses a gloved finger to separate the amniotic sac from the uterus, are said to induce labor in 1 in 8 woman, although some people argue that labor would have begun regardless of whether a membrane sweep was performed or not (and the same can be said about at-home methods). In short, don’t worry, you’ll most likely go into labor when your body is ready. 

Can You Predict When You Might Go Into Labor?

If you’re reading this in anticipation of your own delivery day, you might be looking for signs that the time is near. But having symptoms—or even the lack of—doesn’t necessarily mean labor is starting soon. “Sometimes—not always—you may have signs that your body is preparing for labor,” says Dr. Evans. 

“You might notice a change in the discharge from your vagina or a few cramps in your abdomen. You may have a low, dull ache in your back that can come and go. You may also feel pressure in your vagina,” she explains. Even dilation isn’t a sure thing. While your doctor may perform a cervical check several weeks before your due date, not even dilation can predict how soon labor will begin.

It can be frustrating, but often the only way to know that delivery day is around the corner is once contractions begin with consistency, or your water breaks. Until then, think of your due date as a guide rather than a guaranteed ending. And while it might feel like you’re enduring a never-ending pregnancy, it definitely won’t last forever. 

So, How Do You Deal?

While patience might be in short supply, when waiting to go into labor it’s best to take each day as it comes. “I think when you’re struggling you have an ‘end date’ in mind and when that date comes and goes, it’s so hard. It’s probably best to set the ‘end date’ in your mind as 41 weeks (as opposed to 40 weeks) to avoid disappointment,” suggests Seifert. 

“My advice is to treat yourself every day that you go past. Every day that I went past my due date, I treated myself to something fantastic. A special lunch, a new pair of pajamas, anything!” says Seifert. However difficult it might be to watch the days tick by with no sign of labor, try to enjoy these pre-baby days, because they are definitely numbered. When the baby does arrive—even if it feels long overdue—all that waiting will finally feel worth it.

Pregnant woman holding her stomach on a bed with a plant in the background

Want evidence-based health & wellness advice for fertility, pregnancy, and postpartum delivered to your inbox?

Your privacy is important to us. By subscribing you agree to our Privacy Policy and Terms & Conditions.

Expectful uses only high-quality sources, including academic research institutions, medical associations, and subject matter experts.

  1. CDC"National Vital Statistics Reports ", vol. 67, no. 8Nov 7, 2018https://www.cdc.gov/nchs/data/nvsr/nvsr67/nvsr67_08-508.pdf.

  2. William A. Grobman, M.D., Madeline M. Rice, Ph.D., Uma M. Reddy, M.D., M.P.H., Alan T.N. Tita, M.D., Ph.D., Robert M. Silver, M.D., Gail Mallett, R.N., M.S., C.C.R.C., Kim Hill, R.N., B.S.N., Elizabeth A. Thom, Ph.D., Yasser Y. El-Sayed, M.D., Annette Perez-Delboy, M.D., Dwight J. Rouse, M.D., George R. Saade, M.D."Labor Induction versus Expectant Management in Low-Risk Nulliparous Women"The New England Journal of Medicine, vol. 379Aug 9, 2018, pp. 513-523https://www.nejm.org/doi/full/10.1056/nejmoa1800566.

  3. David A Savitz, James W Terry Jr, Nancy Dole, John M Thorp Jr, Anna Maria Siega-Riz, Amy H Herring"Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination"American Journal of Obstetric Gynocology, vol. 187, no. 6Dec 1, 2002, pp. 1660-6https://pubmed.ncbi.nlm.nih.gov/12501080/.

  4. Debby Amis, RN, BSN, CD(DONA), LCCE, FACCE"Healthy Birth Practice #1: Let Labor Begin on Its Own"The Journal of Perinatal Education, vol. 23, no. 4Oct 1, 2014, pp. 178–187https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4235056/#:~:text=Many%20scientists%20now%20believe%20that,%2C%20%26%20Mendelson%2C%202004)..

  5. Rebecca Dekker, PhD, RN" The Evidence on: Due Dates"Evidence Based Birthhttps://evidencebasedbirth.com/evidence-on-due-dates/.

  6. "Pregnancy at Age 35 Years or Older"ACOG, vol. 11Aug 1, 2022https://www.acog.org/clinical/clinical-guidance/obstetric-care-consensus/articles/2022/08/pregnancy-at-age-35-years-or-older#:~:text=We%20recommend%20proceeding%20with%20delivery,stillbirth%20beyond%20this%20gestational%20age..


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