Your true due date: The low-down on when to really expect baby

pregnancy due date

The term “due date” is a misnomer. 

Your library book has a due date, your final paper has a due date, your status report for work has a due date.

But a baby? No such thing. The “due date” is the middle date of the four week time period (38-42 weeks) during which most women give birth. I prefer to refer to it as the “40th week” date.

Tip: Did you know that for 1st births, the “due date” can be on average a week later than for consequent births? (See Heart and Hands, by Elizabeth Davis.)

This date is often miscalculated when:

  1. You don’t know the first day of your last menstrual period (LMP), or
  2. You know your LMP, but your menstrual cycle was not 28 days.

Why does this matter?

  1. We want to know the right window of “when to expect.” It is empowering to know that, with a healthy pregnancy, you will likely give birth during the 38-42 week window. With inaccurate dating, women are often disappointed, thinking their baby “should have come already” when it’s perfectly normal for baby to keep growing inside of you.
  2. Avoiding unnecessary inductions. Women might be geared toward inductions based solely on the date, such as 41 weeks. But oftentimes this date is miscalculated, so they might be trying to induce you at an even earlier date. Knowing this date can help you plan with your care provider.
  3. Knowing if it’s a preemie. A baby born before 36/37 weeks is defined as a preemie, and will likely need special care after birth.


I) Most Accurate of All:

    If you had an ultrasound before week 11, you can use the estimated due date (EDD) from the ultrasound. This is considered extremely accurate – the earlier, the more accurate. Ultrasound dating after week 11 is not reliable, because by that point the embryo’s too big to be statistically accurate for everyone – like comparing the average body size of an Asian with an average Swede – hello?
    If your menstrual cycle prior to pregnancy was usually 28 days, calculate using the first day of your Last Menstrual Period (LMP) with any “Due Date Calculator” online.

2) Pretty Darn Accurate:

    Since due dates are based on a 28-day menstrual cycle, WWYD if your cycle was not 28 days? No problem: Just add or subtract the number of days’ difference to calculate accordingly.  For example, if your cycle was 35 days, add 7 days to the first day of your last period (LMP).  If your cycle was 25 days, subtract 3 days from LMP,.  Any due date calculator online calculates using the First Day of Last Menstrual Period (LMP), so use your adjusted LMP to get the most accurate “due date” (40th week day) for your baby.

3) So-So Accuracy:

  • Date of Positive Pregnancy Test. A pregnancy blood test will register positive by one week after conception, and a home pregnancy test (via urine on a stick) will show a positive two weeks after conception, if not earlier.
  • “Love” Dates: If you wrote down your “love” dates, and you know when you were expecting your period, this might give you better insight. Usually, conception happens 14 days before your next period would have arrived. This will not provide you a precise date, but will likely give you the week. Remember, sperm can survive up to 5 days waiting for that egg, but the egg can survive 12-24 hours. Yep!

I wish all of you the most healthy pregnancy, however long or short it may be. The true due date for healthy pregnancies is whenever your baby is ready.


© Pamela Hodson |

One thought on “Your true due date: The low-down on when to really expect baby

  1. Hi Chaya! I missed the event at your home last week because the woman I am too accompany was having contractions. Well, we are still here a week later and I enjoyed reading your post about “due dates!”
    May we meet at many joyous occasions!
    Kol tuv,
    Chava Dumas

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