How to Read Your CGM Data: A Beginner's Guide

Starting out with a continuous glucose monitor can feel like learning a new language — numbers, arrows, graphs, and alerts all at once! But once you understand the basics, your CGM becomes one of the most powerful tools in your diabetes management toolkit. This beginner's CGM data reading guide will walk you through everything you need to know, step by step.

What Is a CGM and What Does It Measure?

A continuous glucose monitor (CGM) is a small wearable device that tracks your blood sugar levels throughout the day and night, automatically. Instead of a single snapshot like a fingerstick, your CGM gives you a continuous picture of how your glucose is moving.

• Measures glucose levels in the fluid just under your skin

• Takes readings every 1 to 5 minutes depending on the device

• Sends data wirelessly to a receiver, phone, or smartwatch

• Works around the clock — even while you sleep

Understanding Your Glucose Numbers

Your CGM displays your current glucose level as a number, usually in mg/dL. Most healthcare providers suggest a target range of 70–180 mg/dL for many people with diabetes, but your personal targets may differ.

• Below 70 mg/dL is generally considered low (hypoglycemia)

• 70–180 mg/dL is the commonly recommended target range

• Above 180 mg/dL is considered high (hyperglycemia)

• Always follow your doctor's personalized glucose goals

What the Trend Arrows Mean

Those little arrows next to your glucose number are incredibly helpful — they show you which direction your blood sugar is heading right now. Learning to read them helps you act before a high or low becomes a problem.

• Straight right arrow: glucose is stable and holding steady

• Single arrow up or down: glucose is rising or falling slowly

• Double arrows up or down: glucose is changing rapidly — act quickly

• Use trend arrows alongside your number, not instead of it

Reading Your Glucose Graph Over Time

The graph on your CGM app or receiver shows your glucose curve over the past few hours. A smooth line staying within your target range is exactly what you're aiming for — big spikes and dips are worth noting and discussing with your care team.

What Is Time in Range and Why It Matters

Time in Range (TIR) is the percentage of time your glucose stays within your target zone, and it's becoming one of the most important metrics in diabetes care. Many experts recommend aiming for at least 70% TIR, though your doctor will set your personal goal.

• Higher TIR is linked to better long-term health outcomes

• Review your TIR daily, weekly, and monthly for trends

• Share your TIR reports with your healthcare provider

• Most CGM apps generate TIR reports automatically

Common CGM Alerts and What to Do

Your CGM can be set to alert you when glucose goes too high or too low, giving you precious time to respond. Getting comfortable with your alert settings means fewer surprises and more peace of mind every day.

• Low glucose alert: eat a fast-acting carb and recheck in 15 minutes

• High glucose alert: hydrate, check for causes, and follow your care plan

• Urgent low alert: treat immediately — this needs fast action

• Calibration or sensor alerts: follow your device's specific instructions

Shop Diabetes Supplies at MDS Diabetes

Ready to get more out of your CGM journey? MDS Diabetes carries a trusted selection of CGM supplies and diabetes management products to keep you equipped and confident. Visit us at mdsdiabetes.com or give our friendly team a call at (877) 861-3571 — we're here to help you thrive every step of the way.