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CGM · Glucose Management Indicator

GMI to A1C Calculator

Convert your Glucose Management Indicator (GMI) into mean glucose and estimated A1C, or work backwards from your CGM mean glucose to GMI. Includes the GMI formula and a full GMI to A1C chart.

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GMI to A1C conversion chart

Mean glucose (CGM) converted to GMI and estimated A1C. Your A1C lab result is the reference standard for clinical decisions.

Mean Glucose (mg/dL)Mean Glucose (mmol/L)GMI (%)Est. A1C (%)
804.45.2%4.4%
905.05.5%4.8%
1005.55.7%5.1%
1106.15.9%5.5%
1206.76.2%5.8%
1307.26.4%6.2%
1407.86.7%6.5%
1508.36.9%6.9%
1608.97.1%7.2%
1709.47.4%7.6%
18010.07.6%7.9%
19010.57.9%8.2%
20011.18.1%8.6%
21011.78.3%8.9%
22012.28.6%9.3%
23012.88.8%9.6%
24013.39.1%10.0%
25013.99.3%10.3%
26014.49.5%10.7%
27015.09.8%11.0%
28015.510.0%11.4%
29016.110.2%11.7%
30016.610.5%12.1%
31017.210.7%12.4%
32017.811.0%12.8%

What is GMI and how does it compare to A1C?

The Glucose Management Indicator (GMI) is a percentage calculated from your continuous glucose monitor's average glucose over the past 10–14 days. It replaces the older term "estimated A1C" for CGM users, because the estimate is derived from sensor data rather than a blood sample. The GMI formula is GMI (%) = 3.31 + 0.02392 × mean glucose in mg/dL.

GMI and A1C are closely related — both translate average glucose into a familiar percentage — but they measure different windows. A1C reflects roughly three months of glycated hemoglobin, while GMI reflects about two weeks of sensor readings. They can differ by around 0.5% because red blood cell lifespan, iron levels, hemoglobin variants, and sensor calibration all influence the numbers. Use the GMI to A1C calculator to see how your mean glucose maps to both metrics.

GMI to A1C formula

GMI from mean glucoseGMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL)
Mean glucose from GMIMean glucose (mg/dL) = (GMI − 3.31) ÷ 0.02392

For example, a CGM mean glucose of 154 mg/dL gives a GMI of 3.31 + 0.02392 × 154 = 7.0%. Using the ADAG formula, the same mean glucose estimates an A1C of about 6.5% — close, but not identical. This is why GMI and A1C can show different numbers on the same day.

GMI to A1C — frequently asked questions

What is GMI (Glucose Management Indicator)?

GMI is an A1C-like percentage derived from your continuous glucose monitor (CGM) mean glucose over the past 10–14 days. It uses the formula GMI (%) = 3.31 + 0.02392 × mean glucose in mg/dL.

How to convert GMI to A1C?

GMI and A1C both estimate average glucose, but they use different formulas. To compare them, convert GMI to mean glucose first (divide GMI minus 3.31 by 0.02392), then estimate A1C with the ADAG formula A1C = (glucose + 46.7) ÷ 28.7. The chart on this page does this for common values.

Is GMI the same as A1C?

No. GMI is calculated from CGM data over about two weeks, while A1C is a lab test of glycated hemoglobin reflecting three months. They usually agree closely, but can differ by about 0.5% due to red blood cell lifespan, sensor calibration, and other factors.

What is a good GMI?

A GMI under 6.0% is generally considered good control. GMI of 6.0–7.0% reflects moderate control, and higher values indicate more time above target. Discuss your personal GMI target with your clinician.

How do I calculate GMI from my CGM?

Take the mean glucose reported by your CGM (in mg/dL) and apply GMI (%) = 3.31 + 0.02392 × mean glucose. For example, a mean glucose of 154 mg/dL gives a GMI of about 7.0%.

Related tools

New to the basics? Read our what is A1C guide, use the interactive A1C to eAG calculator, or browse every value in the A1C to eAG conversion chart.