Enter the average glucose your CGM app reports for the last 14 to 90 days, in mg/dL or mmol/L, and see the glucose management indicator (GMI) it predicts: the A1C your sensor data points to, in percent and mmol/mol. Or type a GMI and read off the average glucose behind it. Any one field updates the other three.
What is GMI?
The glucose management indicator is the A1C your CGM data predicts. It was defined in 2018 (Bergenstal et al., Diabetes Care 2018) by fitting a straight line between the mean glucose of continuous glucose monitors and laboratory A1C in study participants, and it replaced the older "estimated A1C" label on CGM reports. Your CGM app computes it from the average of every reading in the window you pick, usually 14, 30 or 90 days, and prints it on the same percent scale as a lab A1C so the two can be read side by side.
That is also what this GMI calculator does: it does not measure anything, it applies the published line to the average you enter. Where the A1C in your lab report reflects glucose bound to hemoglobin over about three months, GMI reflects the glucose your sensor actually saw over the days you chose, with no red-cell biology in the way.
GMI to A1C: how the two relate
There is no conversion between GMI and A1C, because GMI is already expressed on the A1C scale: a GMI of 7.0 percent is meant to be read the way a lab A1C of 7.0 percent would be. The conversion this page performs is the one underneath, from a CGM average glucose to the GMI it predicts. Every 25 mg/dL (about 1.4 mmol/L) of average glucose adds roughly 0.6 to the GMI.
GMI and a lab A1C still disagree in many people, and that is expected. In the study that defined GMI the two matched exactly in 19 percent of participants, differed by 0.3 points or more in 51 percent and by 0.5 points or more in 28 percent. The usual reasons are the different time windows, red blood cells that live longer or shorter than average, anemia, kidney or liver disease, and hemoglobin variants that interfere with some assays. Our GMI vs A1C guide walks through each one and what to do about the gap.
GMI conversion chart
Average glucose in both units with the GMI it predicts, in percent and mmol/mol, from 100 to 300 mg/dL in steps of 10, all from the published formula and rounded the way the calculator rounds.
| Average glucose (mg/dL) | Average glucose (mmol/L) | GMI (%) | GMI (mmol/mol) |
|---|---|---|---|
| 100 | 5.6 | 5.7 | 39 |
| 110 | 6.1 | 5.9 | 41 |
| 120 | 6.7 | 6.2 | 44 |
| 130 | 7.2 | 6.4 | 47 |
| 140 | 7.8 | 6.7 | 49 |
| 150 | 8.3 | 6.9 | 52 |
| 160 | 8.9 | 7.1 | 55 |
| 170 | 9.4 | 7.4 | 57 |
| 180 | 10.0 | 7.6 | 60 |
| 190 | 10.5 | 7.9 | 62 |
| 200 | 11.1 | 8.1 | 65 |
| 210 | 11.7 | 8.3 | 68 |
| 220 | 12.2 | 8.6 | 70 |
| 230 | 12.8 | 8.8 | 73 |
| 240 | 13.3 | 9.1 | 75 |
| 250 | 13.9 | 9.3 | 78 |
| 260 | 14.4 | 9.5 | 81 |
| 270 | 15.0 | 9.8 | 83 |
| 280 | 15.5 | 10.0 | 86 |
| 290 | 16.1 | 10.2 | 88 |
| 300 | 16.7 | 10.5 | 91 |
What is a good GMI?
Because GMI sits on the A1C scale, the same general goal applies: the American Diabetes Association names 7 percent or less as the target for most people living with diabetes, and the right number for you is individual. A low GMI earned with frequent lows is not a win, so read it next to time in range and time below range, and give it at least 14 days of data with the sensor active about 70 percent of the time before you trust it. The GMI vs A1C guide has a band-by-band table.
The formulas behind this page
- GMI (%) = 3.31 + 0.02392 x mean glucose (mg/dL), from the study that defined the glucose management indicator. Bergenstal et al., Diabetes Care 2018
- Mean glucose (mg/dL) = (GMI - 3.31) / 0.02392, the same line solved for glucose, which is how a GMI you type turns back into an average.
- mmol/L to mg/dL: multiply by 18.016 (the molar mass of glucose), and divide to go the other way.
- GMI in mmol/mol = (GMI% - 2.15) x 10.929, the standard NGSP to IFCC conversion used for A1C.
- The older estimated A1C used the ADAG line (eAG = 28.7 x A1C - 46.7), which is what our A1C calculator uses for a lab A1C. The two lines agree around 154 mg/dL and drift apart at higher averages.
Sugar Sense shows GMI next to your average glucose and time in range in Statistics, computed from your connected CGM with the same formula, free.
Frequently asked questions
Can you convert GMI to A1C?
There is nothing to convert: GMI is already expressed on the A1C scale. A GMI of 7.0 percent is meant to be read the way a lab A1C of 7.0 percent would be. What the calculator on this page converts is your CGM average glucose into that GMI, using the formula from the 2018 study that defined it, GMI = 3.31 + 0.02392 × mean glucose in mg/dL. The lab A1C and the GMI can still differ, and the gap is biology, not arithmetic.
Is a GMI of 6.2% good?
Read on the A1C scale, 6.2 percent sits below the 7 percent or less that the American Diabetes Association names as the general target for most people living with diabetes, and it corresponds to a CGM average of about 121 mg/dL (6.7 mmol/L). Whether it is good for you depends on how you got there: a low GMI with frequent lows is not a win, which is why GMI is always read next to time in range and time below range. Targets are individual; agree yours with your care team.
What is more accurate, GMI or A1C?
They measure different things, so neither is the wrong one. A lab A1C is the clinical reference: it reflects glucose bound to hemoglobin over roughly the last two to three months and is what diagnosis and most guidelines rest on. GMI reflects the glucose your sensor actually recorded over the period you chose, updated whenever you look, with no red-cell biology in the way. In the study that defined GMI the two matched exactly in 19 percent of people, differed by 0.3 points or more in 51 percent and by 0.5 points or more in 28 percent, so a gap is normal, not a sign that either number is broken.
How many days of CGM data does GMI need?
The international consensus on CGM metrics recommends at least 14 days of data with the sensor active about 70 percent of the time before reading GMI or time in range. A few days, or a patchy fortnight with long gaps, can swing the average and the GMI with it. Most CGM apps report GMI for 14, 30 and 90 day windows; use the same window when you compare it with a lab A1C.
Why is my GMI higher or lower than my lab A1C?
Because A1C depends on red blood cells and GMI does not. Anything that changes how long red cells live or how the hemoglobin reads in the assay moves the lab A1C without moving your glucose: iron-deficiency anemia can read falsely high, kidney or liver disease can distort the result, and hemoglobin variants interfere with some methods (NIDDK). People also simply glycate at different rates. The two time windows differ too: a calm two weeks after a rough two months gives a GMI below the A1C. Our GMI vs A1C guide walks through each cause.
Is GMI the same as estimated A1C (eA1C)?
Same idea, updated formula. CGM reports used to print an estimated A1C computed with the ADAG line that our A1C calculator uses. In 2018 the metric was renamed glucose management indicator and given its own line fitted to CGM data, so the two agree closely around 154 mg/dL (both about 7.0 percent) and drift apart at higher averages: at 200 mg/dL the ADAG line gives about 8.6 percent while GMI gives about 8.1 percent. The rename also made the point that the number is an indicator, not a substitute for the lab test.
Does Sugar Sense show GMI?
Yes. Sugar Sense shows GMI next to your average glucose and time in range in Statistics for the last 7, 30 and 90 days, computed from your connected FreeStyle Libre, Dexcom or Nightscout readings with the same published formula as this page, and it is free.
More free tools
- Blood Sugar Converter: mmol/L to mg/dL and Back
- A1C Calculator: Convert A1C to Average Glucose
- Time in Range Calculator
- Fructosamine to A1C Calculator
- Blood Glucose Log: Free Printable Log Sheet (PDF)
This tool is for education only. It is not medical advice, it does not replace laboratory testing, and it must never be used for insulin dosing or other treatment decisions. Always work with your healthcare team. See our full medical disclaimer.
