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GMI to A1C Calculator
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This tool gives an estimate for education only. It is not medical advice. Glucose readings, lab methods, and individual factors can shift the numbers, so confirm any result with a clinician or a laboratory A1C test before making health decisions.
Example: GMI 7.0% — mean glucose 154.3 mg/dL, estimated A1C 7.0%.
Behind the numbers
How GMI converts to A1C
GMI is an estimate of A1C based on average glucose from a continuous glucose monitor, usually over 10 to 14 days. The standard GMI formula is GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL). The long-used estimated average glucose (eAG) formula is eAG (mg/dL) = 28.7 × A1C (%) − 46.7. To go from GMI to A1C, this calculator first solves the GMI formula for mean glucose, then converts that glucose to an A1C using the eAG formula in reverse. To go the other way, it converts A1C to eAG, then eAG to GMI.
For a GMI of 7.0%: mean glucose = (7.0 − 3.31) ÷ 0.02392 = 154.3 mg/dL. Then estimated A1C = (154.3 + 46.7) ÷ 28.7 = 7.00%. In the other direction, an A1C of 6.5% gives eAG = 28.7 × 6.5 − 46.7 = 139.8 mg/dL, and GMI = 3.31 + 0.02392 × 139.8 = 6.66%.
Examples
Example conversions
| GMI (%) | Mean glucose (mg/dL) | Estimated A1C (%) |
|---|---|---|
| 6.0 | 112.5 | 5.55 |
| 6.5 | 133.4 | 6.27 |
| 7.0 | 154.3 | 7.00 |
| 7.5 | 175.2 | 7.73 |
| 8.0 | 196.1 | 8.46 |
| 9.0 | 237.9 | 9.92 |
Tips
GMI reflects roughly the last two weeks of sensor glucose, while a lab A1C reflects about two to three months — short-term changes move GMI faster than A1C.
If your GMI and lab A1C differ by more than about 0.5%, ask your clinician about possible causes, such as anemia, kidney issues, or sensor gaps.
Use at least 10 to 14 days of sensor data, with the sensor worn most of the time, for a GMI you can trust.
Do not change medication or insulin doses based on a GMI estimate alone — confirm with a lab A1C and your clinician first.
Good to know
Frequently asked questions
What is GMI?
GMI, the Glucose Management Indicator, is an estimated A1C calculated from average glucose measured by a continuous glucose monitor. It is reported as a percentage, like A1C, but it is derived from sensor data rather than a blood test.
Is GMI the same as A1C?
No. GMI estimates what the A1C would be from recent average glucose, while a lab A1C measures glycated hemoglobin in the blood over two to three months. They usually track closely, but they can differ, especially when glucose has changed recently or when conditions affect red blood cells.
What is a good GMI?
For most adults with diabetes, a common target is a GMI below 7.0%, matching the usual A1C goal — but targets are personal. Your clinician sets the right target for your age, health, and treatment plan.
Why does my GMI differ from my lab A1C?
They cover different time spans, and sensor readings, missing data, and factors like anemia or recent blood loss can shift either number. A gap under about 0.5% is common; a larger gap is worth discussing with your clinician.