CGM · Glucose Management Indicator

GMI to A1C Calculator

This GMI to A1C calculator converts your Glucose Management Indicator (GMI) into mean glucose and an estimated A1C, or works backwards from your CGM mean glucose to GMI. It includes the GMI formula and a full conversion chart.

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How to use the GMI to A1C calculator

Two tabs, one set of formulas. Start with whichever number your device reports.

  1. GMI to glucose: enter the GMI percentage shown in your CGM app, for example 7.0, and press Calculate. You get the matching mean glucose and an estimated A1C.
  2. Glucose to GMI: switch to the Glucose to GMI tab and enter your sensor's mean glucose in mg/dL or mmol/L to see the corresponding GMI.
  3. Compare the two metrics: GMI and A1C use different formulas, so they can differ by about 0.5%. Use both numbers to spot trends, not as exact substitutes.
Worked example

A mean glucose of 154 mg/dL gives a GMI of 3.31 + 0.02392 × 154 = 7.0%. The same average converts to an estimated A1C of about 7.0% with the ADAG formula, which is why the two metrics usually tell a similar story.

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 (%)
80 4.4 5.2% 4.4%
90 5.0 5.5% 4.8%
100 5.5 5.7% 5.1%
110 6.1 5.9% 5.5%
120 6.7 6.2% 5.8%
130 7.2 6.4% 6.2%
140 7.8 6.7% 6.5%
150 8.3 6.9% 6.9%
160 8.9 7.1% 7.2%
170 9.4 7.4% 7.6%
180 10.0 7.6% 7.9%
190 10.5 7.9% 8.2%
200 11.1 8.1% 8.6%
210 11.7 8.3% 8.9%
220 12.2 8.6% 9.3%
230 12.8 8.8% 9.6%
240 13.3 9.1% 10.0%
250 13.9 9.3% 10.3%
260 14.4 9.5% 10.7%
270 15.0 9.8% 11.0%
280 15.5 10.0% 11.4%
290 16.1 10.2% 11.7%
300 16.6 10.5% 12.1%
310 17.2 10.7% 12.4%
320 17.8 11.0% 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, and 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 glucose GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL)
Mean glucose from GMI Mean 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 7.0% too. GMI and A1C can still show different numbers on the same day, because they measure different windows of time.

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%.

Key takeaways

  • GMI is an A1C-like percentage derived from your CGM mean glucose over the past 10 to 14 days, using GMI (%) = 3.31 + 0.02392 × mean glucose.
  • GMI and A1C both estimate average glucose but use different formulas and windows, so they can differ by about 0.5%.
  • The lab A1C test remains the reference standard for diagnosis and treatment decisions; GMI is a tracking metric between visits.
  • A mean glucose of 154 mg/dL maps to a GMI of 7.0% and an estimated A1C of about 7.0%.
  • Use the chart on this page to convert common mean glucose values, and confirm trends with your clinician.

Conclusion

GMI gives CGM users a familiar percentage to track between lab visits, but it is not a replacement for the A1C blood test. Convert your sensor's mean glucose with this GMI to A1C calculator, compare the result against your last lab value, and let any gap between the two prompt a conversation with your care team rather than a guess. When you do get a new A1C result, translate it into everyday glucose numbers with the A1C calculator or the A1C to eAG conversion chart.

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.