CGM Accuracy Comparison 2025: Dexcom G7 vs FreeStyle Libre 3 vs Medtronic Simplera

Continuous glucose monitors (CGMs) have transformed diabetes management, offering real-time glucose tracking without the need for frequent fingersticks. However, accuracy is critical—an unreliable CGM can lead to incorrect insulin dosing and health risks. This post compares the accuracy of three leading CGM sensors: Dexcom G7, FreeStyle Libre 3, and Medtronic Simplera, based on a recent study.

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Study Methodology

The study, led by Eichenlaub et al. (2025) and published in the Journal of Diabetes Science and Technology, conducted a head-to-head comparison using 24 adults with type 1 diabetes. Each participant wore all three sensors simultaneously on their upper arms for about two weeks. Dexcom G7 sensors were replaced on day 5, Simplera on day 8, while FreeStyle Libre 3 lasted the full period. This was due to their different wear limits and to ensure that the data covered the intended wear life of each product.

Testing Procedures

Participants underwent three 7-hour in-clinic testing sessions on days 2, 5, and 15, where glucose levels were measured every 15 minutes using lab-grade devices. Researchers induced controlled glucose fluctuations through meals, insulin dosing, and exercise to evaluate sensor performance under real-life conditions.

Accuracy Measurement: MARD

The study used Mean Absolute Relative Difference (MARD)—the average percentage error between the CGM readings and the lab reference values. A lower MARD indicates better accuracy. The study also examined agreement rate (AR) (percentage of readings within ±20% or ±20 mg/dL of the reference) and error grid analysis to assess potential misguiding errors in insulin management.

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Accuracy Results

Overall MARD Comparison

Against the most precise lab reference (YSI analyzer):

• FreeStyle Libre 3: 11.6%
• Dexcom G7: 12.0%
• Medtronic Simplera: 11.6%

Against a standard fingerstick meter (Contour Next):

• Libre 3 and Dexcom G7: ~9.7–10.1%
• Simplera: 16.6% (indicating greater variability)

Libre 3 and Dexcom G7 demonstrated consistent accuracy across different reference methods, while Simplera was less reliable when compared to fingerstick meters. This suggests that in more everyday conditions (like comparing to your home glucose meter), Dexcom G7 and Libre 3 remained consistently accurate, while Simplera tended to deviate more from the meter readings.

Accuracy Across Glucose Ranges

• Normal & High Glucose: Dexcom G7 and Libre 3 performed best, closely tracking post-meal spikes.
• Low Glucose: Medtronic Simplera excelled, detecting hypoglycemia more accurately.
• Rapid Changes: Dexcom G7 and Libre 3 maintained steady performance, while Simplera struggled during fast glucose rises but was better at detecting rapid drops.

In practical terms, Dexcom G7 and Libre 3 handled high sugars slightly more accurately – for example, during post-meal spikes, their readings tracked closer to the reference. Medtronic Simplera, on the other hand, had an edge when glucose dropped low – it tended to track the true low values more closely than the other two in those hypoglycemic moments. This trade-off means each device shines in different scenarios.

First-Day Accuracy

If you’ve worn CGMs, you might know sensors can be less accurate on the first day of use as they “warm up” or acclimate.

• Libre 3: Most stable from the start (MARD ~10.9%)
• Dexcom G7: Slightly higher initial MARD (~12.8%)
• Simplera: Least reliable on day 1 (MARD ~20.0%), improving significantly afterward

This study captured that effect: Medtronic Simplera was notably less accurate in the first 12 hours of wear. In that initial period, Simplera’s MARD was about 20.0%, meaning a lot of early readings could be quite off​ Dexcom G7’s first 12-hour MARD was around 12.8%, and Libre 3’s was around 10.9%, indicating both were more stable out of the gate​.

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Alerts & Reliability

Low Glucose Detection

• Simplera: Detected 93% of lows, outperforming Dexcom G7 (80%) and Libre 3 (73%)
• Drawback: Higher false alarms for lows

High Glucose Detection

• Dexcom G7 & Libre 3: Caught ~99% of high glucose events, outperforming Simplera (85%)
• Simplera: Fewer false highs but sometimes missed actual highs

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Discussion: Which CGM Performs Best?

Strengths & Weaknesses

Real-World Considerations

• Libre 3 and Dexcom G7 performed slightly better overall, making them the top choices for most users
• Simplera is ideal for those prone to hypoglycemia but has more inconsistent readings
• All three CGMs meet regulatory accuracy standards, meaning they are according to the study safe for insulin dosing decisions

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Conclusion

This head-to-head comparison confirms that Dexcom G7 and FreeStyle Libre 3 are the most accurate CGMs, with consistent performance across various glucose levels. Medtronic Simplera stands out for detecting lows effectively but is less reliable for high glucose and takes longer to stabilize after insertion.

Choosing the best CGM depends on individual needs: If hypoglycemia detection is a priority, Simplera is a strong choice. If consistent accuracy and high-glucose tracking matter most, Dexcom G7 and Libre 3 are better options. Regardless of the sensor, CGMs remain invaluable tools for diabetes management, helping users make informed decisions and improve glucose control.

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Want to gain more insights from your CGM? Try SNAQ.AI. The app seamlessly connects with Dexcom G7 and FreeStyle Libre 3.

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Sources are the original study by Eichenlaub et al., 2025, Journal of Diabetes Science and Technology.

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