How Pregnancy Is Counted (and Why It’s So Confusing): Weeks, Months, and What They Actually Mean

Pregnancy is one of the only times in life where we’re asked to think in weeks instead of months, and for many people, it’s confusing, frustrating, and sometimes anxiety-provoking.

In this episode, we break down how pregnancy is actually counted, why clinicians use weeks and days instead of months, and how to make sense of phrases like “halfway there,” “almost seven months,” or “full term.” We also explain where these conventions came from, what they’re used for medically, and how patients can translate them into something that feels more intuitive and human.

If you’ve ever wondered:

• Why pregnancy is 40 weeks but “nine months”

• Why doctors talk in weeks and days

• What “halfway” really means

• Or why your app, your provider, and your friends all seem to be using different math

This episode is for you.

At Maternal Resources, we believe understanding your body and your pregnancy shouldn’t feel like decoding a foreign language. Clear information is a form of care.

What You’ll Learn in This Episode

• How pregnancy is dated and why it starts before conception

• Why weeks (not months) matter for medical decision-making

• How months map onto weeks and where the confusion comes from

• What people mean when they say “halfway through pregnancy”

• How due dates are estimates, not expiration dates

• How to think about pregnancy in a way that’s both medically accurate and emotionally grounded

Pregnancy Counting, Explained

Weeks and days are the medical language of pregnancy.
Clinicians count pregnancy from the first day of the last menstrual period, not from conception. That’s because ovulation and implantation vary, but menstrual cycles give us a consistent starting point. Using weeks allows for precision when it comes to growth, development, testing windows, and clinical decision-making.

Months are less precise and that’s where confusion begins.
Calendar months don’t divide evenly into pregnancy. Some months have four weeks, some have more. That’s why “nine months pregnant” can mean different things depending on how you’re counting.

So what about being “halfway”?
Halfway through pregnancy is around 20 weeks, not five months. This is often when people have anatomy scans and start to feel more connected to the pregnancy, which adds to the emotional weight of that milestone.

Due dates are estimates, not deadlines.
Only a small percentage of babies are born on their exact due date. Pregnancy is a range, not a single day, and understanding that can help reduce unnecessary stress.

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https://www.maternalresources.org/

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