Understanding GMI vs Laboratory A1C
GMI stands for Glucose Management Indicator. It was previously referred to as "estimated A1C" on CGM reports. The term was changed to reflect that it is a prediction based on glucose data, not a direct measurement of hemoglobin glycation.
The GMI Clinical Formula
The formula, established by researchers (Bergenstal et al.) for CGM users, is:
GMI (%) = 3.31 + (0.02392 × Average Glucose mg/dL)
Why is my GMI different from my Lab A1C?
It is common for GMI and lab A1C to differ by 0.3% to 0.5%. This happens because A1C is affected by red blood cell lifespan, while GMI is strictly calculated from your 14-day or 30-day glucose data. Both are valuable: A1C for long-term complications risk, and GMI for real-time management adjustment.
Internal Link: Calculate TIR
GMI is most useful when paired with Time in Range (TIR) data. Use our Time in Range Visualizer here.
