Pregnancy is often described as a “9-month journey,” but most doctors and pregnancy apps talk in weeks — which can be confusing for many expecting parents. So how exactly should you count pregnancy: in weeks or months? And why does it matter?
Here’s everything you need to know to track your pregnancy the right way, understand how far along you really are, and prepare for each exciting milestone.
📅 Why Is Pregnancy Counted in Weeks?
While many people think of pregnancy as nine months long, medical professionals count pregnancy in weeks — usually from the first day of your last menstrual period (LMP). This is because:
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Ovulation (and therefore conception) usually occurs about two weeks after your period starts, and that date can be hard to pinpoint precisely.
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Counting from the LMP offers a standardized way to estimate due dates and monitor development.
✅ A full-term pregnancy is considered to be 40 weeks, not exactly 9 months.
📆 How Many Weeks Are in a Month of Pregnancy?
Since months don’t divide evenly into weeks, converting weeks to months isn’t an exact science. But here’s a general breakdown many OB-GYNs and apps use:
| Weeks Pregnant | Months Pregnant |
|---|---|
| 1 – 4 weeks | 1 month |
| 5 – 8 weeks | 2 months |
| 9 – 13 weeks | 3 months |
| 14 – 17 weeks | 4 months |
| 18 – 21 weeks | 5 months |
| 22 – 26 weeks | 6 months |
| 27 – 30 weeks | 7 months |
| 31 – 35 weeks | 8 months |
| 36 – 40 weeks | 9 months |
💡 Pro Tip: You’ll often hear terms like “in your second trimester” instead of months — because it's more medically accurate and consistent.
🤰 Trimesters: Another Way to Track Your Pregnancy
Pregnancy is also divided into three trimesters, each with specific developmental milestones:
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First Trimester (Week 1–13): Your baby is forming all major organs; symptoms like nausea and fatigue are common.
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Second Trimester (Week 14–27): Many women feel their best during this stage. You may start showing and feel the first baby movements.
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Third Trimester (Week 28–40): Your baby grows rapidly, and your body prepares for labor and delivery.
🧮 How to Calculate Your Due Date
To estimate your due date, most providers use Naegelé’s Rule:
First day of your last period + 7 days – 3 months + 1 year = Estimated Due Date
For example, if your last period was on January 10, 2025, your estimated due date would be:
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January 10 + 7 days = January 17
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January 17 – 3 months = October 17
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Add one year = October 17, 2025
📱 You can also use a pregnancy calculator app or ask your provider for an ultrasound to confirm gestational age.
👶 So... Should You Count in Weeks or Months?
✅ Count in weeks when discussing your pregnancy with doctors, using apps, or tracking development — it’s the standard for medical accuracy.
❤️ Use months when casually sharing updates with family and friends who may not understand the weekly system.
📌 Final Thoughts
Understanding how to count pregnancy — whether in weeks, months, or trimesters — helps you stay informed and connected throughout this beautiful journey. While it may seem a bit confusing at first, the 40-week calendar is the most reliable way to monitor your baby’s development, schedule appointments, and prepare for the big day.
Whether you’re 8 weeks, 3 months, or halfway through your second trimester, what matters most is that you feel empowered and supported every step of the way.