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Convert your CGM average glucose (Dexcom, Libre, or other sensor) into GMI — Glucose Management Indicator (%) and IFCC mmol/mol using the Bergenstal 2018 formula. Supports mg/dL and mmol/L. Educational—GMI is not a lab A1C; compare both at clinic visits. More on our medical calculators hub.
Last updated: June 4, 2026
Use 14-day or 90-day average glucose with ≥70% active sensor time. Copy the mean exactly as Clarity or LibreView shows it.
Use ≥14 days of CGM data with ≥70% active time when possible.
GMI estimates lab A1C from glucose averages only. Your drawn HbA1c can differ with anemia, kidney disease, or pregnancy.
Common CGM mean
7.0%
53 mmol/mol
~6.5% teaching anchor
6.3%
≈ 155 mg/dL
7.0%
Elevated mean
7.6%
| Mean glucose (mg/dL) | GMI (%) | IFCC (mmol/mol) | Legacy ADAG A1C (%) | Notes |
|---|---|---|---|---|
| 100 | 5.7% | 39 | 5.1% | Typical fasting non-diabetic teaching range |
| 126 | 6.3% | 46 | 6.0% | Classic “eAG” anchor often cited with ~6.5% threshold |
| 154 | 7.0% | 53 | 7.0% | Common CGM report example → GMI ~7.0% |
| 180 | 7.6% | 60 | 7.9% | Higher average; review TIR and post-meal patterns |
| 200 | 8.1% | 65 | 8.6% | Marked hyperglycemia exposure on average |
| Aspect | GMI (CGM) | Lab HbA1c |
|---|---|---|
| What it measures | Mathematical mean of interstitial glucose readings (CGM) | Percent of glycated hemoglobin on red blood cells (~2–3 month window) |
| Data needed | ≥14 days CGM, typically ≥70% wear time | Venous blood draw, standardized assay |
| Skews GMI vs lab | Sensor error, calibration, compression lows | Anemia, hemolysis, CKD, pregnancy, transfusions, variant hemoglobin |
| Clinical use | Trends between labs, time-in-range context | Diagnosis thresholds, many guideline goals still reference HbA1c |
| Platform | Metric to copy |
|---|---|
| Dexcom Clarity | Average glucose (14-day or custom) |
| FreeStyle LibreView | Glucose profile → average glucose |
| Medtronic CareLink | Summary mean glucose |
| Tidepool / Glooko | Aggregated mean from uploaded CGM |
| Metric | Common teaching goal | Relation to GMI |
|---|---|---|
| Time in Range (70–180 mg/dL) | >70% for many adults | Lower GMI often correlates with higher TIR |
| Time Below Range (<70 mg/dL) | <4% (<54 mg/dL <1%) | Hypoglycemia may not raise mean glucose but harms outcomes |
| GMI | Individualized (often <7% many adults) | Derived from mean glucose, not variability alone |
Mathematical average of interstitial glucose. Responds quickly to the last 2 weeks of wear (or your selected window). Best for day-to-day therapy tweaks with TIR context.
Glycation on red blood cells over their lifespan. Still used for diagnosis (≥6.5%) and many quality metrics. Can disagree with GMI when hematology or kidney disease affects RBCs.
GMI (%) = 3.31 + (0.02392 × mean glucose [mg/dL])
IFCC (mmol/mol) ≈ (GMI − 2.15) × 10.929
mmol/L → mg/dL: multiply by 18.0182
Related: diabetes risk calculator, insulin sliding scale.
Do not adjust insulin or other diabetes drugs from GMI alone. Hypoglycemia, pregnancy, and acute illness need clinician-directed care—not this calculator.
For CGM users comparing Clarity/Libre averages to clinic A1C language
Suggested hashtags: #Type1Diabetes #CGM #Diabetes #Endocrinology #Calculator