This content is for informational purposes only. Always consult your healthcare provider before making health decisions. CGM accuracy data comes from manufacturer-sponsored clinical studies — real-world accuracy may vary.
MARD figures are sourced from manufacturer-published pivotal trial data and peer-reviewed publications as of May 2026. We report overall MARD from the primary accuracy study for each device. Study conditions, reference methods, and populations vary across devices — direct comparison should be made with this in mind.
What MARD means — and why it matters
MARD stands for Mean Absolute Relative Difference. It is the standard accuracy metric for CGM devices, calculated by comparing CGM readings to a reference blood glucose measurement (typically a laboratory glucose analyzer) across many paired readings during a clinical trial.
The formula is simple: for each paired reading, the absolute percentage difference between the CGM reading and the reference is calculated. MARD is the average of those percentage differences across the full study dataset.
Lower MARD = more accurate. A MARD of 7.8% means the device's readings differ from the reference by 7.8% on average. A device with 7.8% MARD is more accurate than one with 9.0% MARD.
MARD is the most widely used accuracy metric because it is scale-independent — it doesn't matter whether glucose is measured in mg/dL or mmol/L. It is also the metric required for FDA clearance submissions.
Important limitation: MARD is reported from controlled clinical studies. Real-world accuracy depends on additional factors including sensor placement, physical activity, altitude, and individual variation.
Compare accuracy and costs across all major CGMs.
Published MARD by device — 2026 data
FreeStyle Libre 3 — 7.9% MARD
The FreeStyle Libre 3 posts a 7.9% MARD in Abbott's published pivotal trial data, making it one of the most accurate prescription CGMs available. It uses the same core sensing platform as the Libre 2 but with a significantly slimmer profile and real-time Bluetooth streaming. Requires a prescription. Read full review →
Abbott Lingo — 7.8% MARD
The Abbott Lingo, Abbott's OTC device, posts a 7.8% MARD — the lowest in the OTC category and competitive with prescription devices. The Lingo is built on the same FreeStyle Libre sensing platform as the Libre 3. No prescription required at ~$49/month.
Dexcom G7 — 8.2% MARD
The Dexcom G7 posts an 8.2% overall MARD, with notably strong performance in the hypoglycemic range (below 70 mg/dL) — a critical accuracy zone for insulin users. The G7 is a prescription device and the clinical standard for users managing insulin-treated diabetes. Read full review →
Dexcom Stelo — 8.7% MARD
The Dexcom Stelo, Dexcom's OTC offering, posts an 8.7% MARD. It shares the G7's sensor technology but is configured for non-insulin-using wellness users. Accuracy is strong for the OTC category and wellness use cases — the higher MARD versus Libre-based devices likely reflects differences in study design and population.
Full accuracy comparison table
| Device | MARD | Sensor life | Monthly cost | Rx required |
|---|---|---|---|---|
| Abbott Lingo | 7.8% | 14 days | ~$49 | No |
| FreeStyle Libre 3 | 7.9% | 14 days | ~$130 | Yes |
| Dexcom G7 | 8.2% | 10 days | ~$350 | Yes |
| Dexcom Stelo | 8.7% | 15 days | ~$99 | No |
MARD figures from manufacturer pivotal trial publications. Monthly costs are retail estimates as of May 2026. Prescription device costs may vary significantly with insurance coverage.
See what the most accurate CGMs cost for 30, 90, or 365 days.
What affects real-world CGM accuracy
Sensor placement
All approved CGMs are worn on the back of the upper arm. Consistent placement in the manufacturer-recommended zone produces the most reliable readings. Placing the sensor on fatty tissue reduces variability.
Compression lows
Sleeping on a sensor can compress the tissue, reducing interstitial fluid flow and producing falsely low readings. This is a hardware limitation of all current CGM designs, not specific to any device.
Calibration
Both Dexcom and Abbott OTC devices are factory-calibrated — no fingerstick is required. Factory calibration eliminates user calibration error, a significant accuracy advantage over older CGM generations.
Altitude
High altitude can affect sensor accuracy for some CGM platforms. Manufacturer guidance typically notes altitude limitations — usually above 10,000 feet — in device documentation.
Extreme temperatures
Very high or very low ambient temperatures can temporarily affect sensor accuracy. All devices should be stored and worn within manufacturer-specified temperature ranges.
Rapid glucose changes
Interstitial glucose lags behind blood glucose by 5–15 minutes. During periods of rapid change — right after meals or during intense exercise — the CGM reading may differ meaningfully from a simultaneous blood glucose measurement.
Accuracy during exercise versus rest
CGM accuracy during exercise has been studied in several device-specific publications. The general finding is that all devices are somewhat less accurate during high-intensity exercise, due to the lag between blood glucose and interstitial glucose being amplified during rapid glucose change.
The Dexcom G7 has published accuracy data specifically during exercise, showing maintained MARD performance within acceptable ranges during moderate exercise. The Abbott Lingo and FreeStyle Libre 3, based on the same platform, show similar performance characteristics.
For athletes who want CGM data during training, all devices listed provide useful directional trend data. The absolute accuracy of any point-in-time reading during intense exercise should be interpreted with the interstitial lag in mind.
Which device is most accurate?
Abbott Lingo — most accurate OTC CGM
At 7.8% MARD, the Abbott Lingo posts the best published accuracy of any CGM available without a prescription — and matches the FreeStyle Libre 3 prescription device closely. For non-prescription users, Lingo delivers accuracy competitive with clinical devices at a fraction of the cost.
Read full Lingo review →FreeStyle Libre 3 — most accurate overall
The FreeStyle Libre 3's 7.9% MARD edges out the G7 (8.2%) across the full dataset. For users who need a prescription CGM, Libre 3 combines strong accuracy with 14-day wear at a lower retail price than the G7. The G7 has stronger accuracy in the hypoglycemic range specifically.
Read full Libre 3 review →Compare all CGM costs for any monitoring period.