A Glucose Management Indicator (GMI) of 6.7% from your continuous glucose monitor estimates that your lab A1C would be around 6.7% and that your average glucose over the reporting period has been roughly 141-146 mg/dL (7.8-8.1 mmol/L). This value straddles the border between prediabetes and early type 2 diabetes and warrants a conversation with your clinician.
What GMI Actually Measures
GMI was introduced by Bergenstal and colleagues in Diabetes Care in 2018 to replace the older term “estimated A1C” (eA1C). The calculation is straightforward: GMI (%) = 3.31 + 0.02392 x mean glucose (mg/dL). For a mean glucose of 144 mg/dL, GMI comes out to 3.31 + 0.02392 x 144 = 6.76%, which rounds to 6.7%. The formula was validated against paired CGM and lab A1C data from hundreds of participants.
The reason the term changed from “estimated A1C” to “GMI” is honest labeling: GMI is a CGM-derived estimate, not a hemoglobin measurement. It can and does differ from the lab A1C, sometimes meaningfully, which confused patients when both numbers shared the same name.
Why GMI and A1C Can Differ
Lab A1C measures the percentage of hemoglobin that has been irreversibly glycated over the lifetime of your red blood cells (about 120 days). GMI measures your actual glucose over 10-14 days of CGM wear. Several factors can push the two apart:
- Red blood cell turnover: faster turnover (iron-deficiency recovery, hemolysis) lowers A1C without changing glucose.
- Recent glucose excursions: a high-stress week at the end of the three-month A1C window can raise A1C above what a brand-new CGM reading shows.
- Hemoglobin variants: HbS, HbC, and others can interfere with A1C assays.
- CGM sensor calibration: consumer sensors typically run with a 10% mean absolute relative difference.
What 6.7% Means on the A1C Scale
If the GMI accurately reflects your A1C, 6.7% is above the 6.5% diabetes diagnostic threshold. The A1C levels guide covers the full scale. A single value is not a diagnosis — the ADA requires confirmation with a second test unless symptoms and glucose values are unambiguous — but it is a clear signal to take action.
GMI, Mean Glucose, and Time in Range
| GMI (%) | Mean glucose (mg/dL) | Mean glucose (mmol/L) | Approx A1C category |
|---|---|---|---|
| 5.7 | 100 | 5.6 | Normal / prediabetes edge |
| 6.0 | 112 | 6.2 | Prediabetes |
| 6.5 | 134 | 7.4 | Diabetes threshold |
| 6.7 | 144 | 8.0 | Early diabetes |
| 7.0 | 154 | 8.6 | ADA target |
| 7.5 | 175 | 9.7 | Above target |
Also pay attention to “time in range” (TIR), the percentage of readings between 70 and 180 mg/dL. Battelino and colleagues’ 2019 consensus recommends more than 70% TIR for most adults with diabetes. A GMI of 6.7% usually corresponds to 60-75% TIR.
How to Lower a 6.7% GMI
The CGM’s continuous data makes it easier to see which foods, times of day, and activities push your glucose up. Common high-yield changes:
- Swap cereal or juice breakfasts for eggs, Greek yogurt, or other protein-forward options.
- Walk 10-15 minutes after your largest meal of the day.
- Cap evening carbohydrates — late-night spikes are common contributors to an elevated mean.
- Prioritize sleep; one short night can raise next-day glucose by 10-20 mg/dL.
- Discuss metformin or other medications with your clinician if you are near the diabetes threshold.
The diet and nutrition hub and the treatment hub cover both lifestyle and pharmacologic approaches in detail.
When to Call Your Clinician
Schedule a visit if your GMI has crossed 6.5% and has stayed there, especially if it is rising over multiple CGM periods. Ask your clinician to run a lab A1C and fasting glucose so you have a confirmed picture. Bring two weeks of CGM data to the visit; this allows a better conversation about patterns, not just a single number.
The Bottom Line
A 6.7% GMI reflects an average glucose of about 144 mg/dL and estimates an A1C of roughly 6.7%. It sits at the early-diabetes threshold. Confirm with a lab test, improve post-meal glucose through food timing and activity, and bring your CGM download to your next appointment. Combined lifestyle and clinical follow-up can usually bring this number back under 6.5%.
