How Accurate Are CGMs? What the Data Really Means

Written By Amanda Davis | BioFit Founder

CGMs are accurate enough to guide behavior but not to diagnose disease.

What “Accuracy” Really Means

Accuracy is measured by MARD (Mean Absolute Relative Difference). MARD shows how close CGM readings are to lab values, which is important for understanding how reliable the device is for tracking glucose trends efficiently.
Most modern CGMs fall between 8–10% in terms of MARD. This means CGM readings are typically within 8–10% of actual blood glucose values. This level of accuracy is excellent for tracking glucose trends over time and ensuring the device's reliability in monitoring changes in glucose levels.

Why CGMs Sometimes Look “Wrong”

  • Compression lows during sleep

  • Rapid glucose changes

  • Sensor warm-up period

  • Dehydration

When to Trust the Data

  • Trend direction

  • Pattern repetition

  • Time-in-range changes

When Not to Panic

One reading does not define your metabolism.

BioFit Rule

We coach decisions based on patterns over time, not on isolated numbers. For example, if you consistently notice higher glucose readings after eating certain meals, that’s a pattern to pay attention to. Recognising these patterns helps tailor your food choices and habits for better glucose control.


Learn how to interpret CGM data with confidence inside the BioFit Edge™.

Amanda Davis | BioFit Founder

Amanda Davis is the founder of BioFit® and the creator of the Certified BioFit Specialist® program. A NASA-trained strategist and fitness innovator, she teaches coaches how to use continuous glucose monitoring (CGM) to deliver smarter, data-driven training.

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What Does a CGM Actually Tell You? [And Why Most People Misread the Data]