Your Due Date Isn’t Accurate And Here’s Why

If you’re expecting, you might have heard that due dates are, well, kind of a joke. The truth is, due dates aren’t that accurate.

Due dates are calculated based on a 28-day menstrual cycle, which not everyone has. In fact, only about 13% of women have a “perfect” 28-day cycle. So if your cycle is shorter or longer than that, your due date might be off by a few days or even a week or two.

But that’s not even the biggest problem: The thing that really throws due dates out the window is the that babies are notoriously unpredictable. Your baby might decide to come early, or they might decide to camp out in there for a little longer than expected. And there’s really no way to know for sure when that’s going to happen.

So is the traditional “due date” really your due date?

Based on the best evidence, there is no such thing as an exact “due date,” and the estimated due date of 40 weeks is not accurate. Instead, it would be more appropriate to say that there is a normal range of time in which most people give birth. About half of all pregnant people will go into labor on their own by 40 weeks and 5 days (for first-time mothers) or 40 weeks and 3 days (for mothers who have given birth before). The other half will not. – Source, Evidence Based Birth

In fact, studies have shown that only about 5% of babies actually arrive on their due date. That means that for the other 95% of us, our due dates are essentially meaningless.

So why do doctors and midwives even bother giving us due dates in the first place? Well, for one thing, it helps them keep track of how your pregnancy is progressing. They can use your due date to schedule ultrasounds and other tests to ensure everything is going smoothly. And if you go past your due date, they might want to induce labor to avoid potential complications.

But as far as predicting when your baby will actually arrive? There’s just no way to know for sure. So if you’re counting down the days until your due date, take it with a grain of salt. Your baby will come when they’re good and ready, no matter what the calendar says.

Focus on taking care of yourself and getting ready for your baby’s arrival, whenever that may be.

• American Pregnancy Association. (2021). Due Date Calculator. Retrieved from https://americanpregnancy.org/due-date-calculator/
• American College of Obstetricians and Gynecologists. (2021). Due Date Calculator. Retrieved from https://www.acog.org/womens-health/faqs/due-date-calculator
• Griffin, T. R., & Abrams, B. (1995). Accuracy of pregnancy dating methods. Obstetrics and Gynecology, 85(2), 212-216. doi: 10.1016/0029-7844(94)00357-S
• Marnach, M. L., Ramin, K. D., Ramsey, P. S., Song, S. W., Stensland, J. J., & An, K. N. (2006). The accuracy of predicting fetal size by ultrasound. Journal of Maternal-Fetal and Neonatal Medicine, 19(12), 767-772. doi: 10.1080/14767050600902146
• Mongelli, M., Wilcox, M., Gardosi, J. (1996). Estimating the date of confinement: Ultrasonographic biometry versus certain menstrual dates. American Journal of Obstetrics and Gynecology, 174(1), 278-281. doi: 10.1016/s0002-9378(96)70439-3