# What is my GMI?

Works out the glucose management indicator (GMI), the A1C level usually seen with a given mean glucose from continuous glucose monitoring (CGM), in percent and mmol/mol, with the Bergenstal 2018 formulas.

- Page: https://www.acalculator.org/health/gmi-calculator
- JSON spec: https://www.acalculator.org/health/gmi-calculator.json
- Version: 16d1c4c7bdf9

## Default answer

Example with the default inputs (Glucose unit mg/dL, Mean glucose (mg/dL) 150): The GMI is 6.9%, or 51.9 mmol/mol.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| units | Glucose unit | The unit of the mean glucose on the CGM report: mg/dL or mmol/L. |
| mgdl | Mean glucose (mg/dL) | The mean glucose from 14 or more days of CGM readings, 90 to 350 mg/dL. |
| mmol | Mean glucose (mmol/L) | The mean glucose from 14 or more days of CGM readings, 5 to 19.4 mmol/L. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| gmi | GMI (%) | GMI = 3.31 + 0.02392 × mean glucose in mg/dL, to 1 decimal. |
| ifcc | GMI (mmol/mol) | GMI = 12.71 + 4.70587 × mean glucose in mmol/L, to 1 decimal. |
| glucoseMmol | Mean glucose (mmol/L) | The typed mg/dL ÷ 18, to 1 decimal. |
| glucoseMgdl | Mean glucose (mg/dL) | The typed mmol/L × 18, to a whole number. |

## Method

GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL); GMI (mmol/mol) = 12.71 + 4.70587 × mean glucose (mmol/L); 1 mmol/L = 18 mg/dL. Each GMI is rounded once to 1 decimal, halves up.

## Assumptions

- The mean glucose comes from at least 10, and preferably 14 or more, days of CGM readings (Bergenstal 2018).
- The formulas come from 528 people with type 1 or type 2 diabetes who wore Dexcom sensors; a lab A1C can differ from the GMI.
- Each result is worked from the exact typed value and rounded once to 1 decimal, halves up.

## Worked examples

1. units = mgdl, mgdl = 150 gives gmi = 6.9%, ifcc = 51.9, glucoseMmol = 8.3. Source: Bergenstal 2018, Table 1: 150 mg/dL gives a GMI of 6.9% (3.31 + 0.02392 × 150 = 6.898).
2. units = mgdl, mgdl = 100 gives gmi = 5.7%, ifcc = 38.9, glucoseMmol = 5.6. Source: Bergenstal 2018, Table 1: 100 mg/dL gives 5.7% (3.31 + 2.392 = 5.702).
3. units = mgdl, mgdl = 350 gives gmi = 11.7%, ifcc = 104.2, glucoseMmol = 19.4. Source: Bergenstal 2018, Table 1: 350 mg/dL gives 11.7% (3.31 + 8.372 = 11.682).
4. units = mmol, mmol = 5 gives ifcc = 36.2, gmi = 5.5%, glucoseMgdl = 90. Source: Bergenstal 2018, Table 1: 5 mmol/L gives 36.2 mmol/mol (12.71 + 23.52935 = 36.23935).
5. units = mmol, mmol = 10 gives ifcc = 59.8, gmi = 7.6%, glucoseMgdl = 180. Source: Bergenstal 2018, Table 1: 10 mmol/L gives 59.8 mmol/mol (12.71 + 47.0587 = 59.7687).
6. units = mmol, mmol = 18 gives ifcc = 97.4, gmi = 11.1%, glucoseMgdl = 324. Source: Bergenstal 2018, Table 1: 18 mmol/L gives 97.4 mmol/mol (12.71 + 84.70566 = 97.41566).
7. units = mgdl, mgdl = 112.5 gives gmi = 6%, ifcc = 42.1, glucoseMmol = 6.3.

## FAQ

### What is the GMI?

The glucose management indicator is an estimate of A1C from the mean glucose of a continuous glucose monitor (CGM). Bergenstal and others named it in 2018 to replace the term "estimated A1C", because the value often differs from a lab A1C and the old name suggested a closer match than there is.

### How is the GMI calculated?

GMI (%) = 3.31 + 0.02392 × the mean glucose in mg/dL. For 150 mg/dL: 3.31 + 3.588 = 6.898, shown as 6.9%. With mmol/L, GMI (mmol/mol) = 12.71 + 4.70587 × the mean glucose in mmol/L. For 8 mmol/L: 12.71 + 37.647 = 50.36, shown as 50.4 mmol/mol.

### Why is my GMI different from my lab A1C?

A lab A1C measures glucose attached to hemoglobin over the life of the red blood cells, about 120 days. The GMI comes from CGM glucose under the skin over the last weeks. In the 528 people behind the formula, the GMI and the lab A1C were the same in 19% of cases, 0.3 points or more apart in 51%, and 0.5 points or more apart in 28% (Bergenstal 2018, Table 3).

### How many days of CGM data do I need?

The authors suggest at least 10, and preferably 14 or more, days of CGM data. Ten days usually give a good mean glucose; 14 days or more give a better picture of low glucose and of variability.

### Is the GMI the same as estimated average glucose (eAG)?

No. They go in opposite directions. eAG turns a lab A1C into an average glucose, from the ADAG study; the A1C calculator on this site does that. The GMI turns a CGM mean glucose into an A1C-like number.

### Which unit should I use?

Use the unit on your CGM report. Each GMI comes from its own formula in the paper: the percent from mg/dL, and mmol/mol from mmol/L. The page changes units with 1 mmol/L = 18 mg/dL.

### When can the GMI and the A1C be far apart?

The paper names a few cases. During a short spell of high glucose (illness, steroids), the GMI runs above a lab A1C taken at the same time. After a short spell of much lower glucose (a new diet or medicine), it runs below. Conditions that change the life span of red blood cells, such as hemoglobin variants and hemolytic anemia, can also explain a gap.

## Sources

- Bergenstal RM, Beck RW, Close KL, et al. Glucose Management Indicator (GMI): a new term for estimating A1C from continuous glucose monitoring. Diabetes Care. 2018;41(11):2275-2280 (both formulas, Table 1, Table 3). https://doi.org/10.2337/dc18-1581 (full text: https://pmc.ncbi.nlm.nih.gov/articles/PMC6196826/, retrieved 2026-10-18)
- PubChem. Glucose, CID 5793: molecular weight 180.16 g/mol, so 1 mmol/L = 18.016 mg/dL, which the page rounds to 18. https://pubchem.ncbi.nlm.nih.gov/compound/5793 (retrieved 2026-10-18)