GMI calculator

GMI (Glucose Management Indicator) is the A1C that usually goes with your average sensor glucose: 3.31 + 0.02392 × your average in mg/dL. An average of 100 mg/dL (5.6 mmol/L) gives a GMI of 5.7%; 154 mg/dL (8.6 mmol/L) gives 7.0%.

Unit

For context: adults without diabetes in one study averaged 99 mg/dL (5.5 mmol/L) on a CGM (Shah et al. 2019), which is a GMI of about 5.7%.

HbA1c ↔ average glucose calculator

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How it is worked out

GMI (%) = 3.31 + 0.02392 × average glucose (mg/dL) GMI (%) = 3.31 + 0.43056 × average glucose (mmol/L)

From Bergenstal et al. 2018, a regression of measured A1C on CGM averages in four studies. It needs 14 days or more of sensor data to be reliable. It isn’t a lab test, and a measured A1C can differ from it. To turn a lab HbA1c into an average glucose, use the HbA1c ↔ average glucose calculator.

Sources

  1. Bergenstal et al. 2018. Diabetes Care 41(11):2275-2280. Glucose Management Indicator (GMI): a new term for estimating A1C from continuous glucose monitoring.
  2. Shah et al. 2019. Journal of Clinical Endocrinology & Metabolism 104(10):4356-4364. CGM profiles in 153 healthy participants without diabetes.
  3. Hutchins et al. 2025. American Journal of Clinical Nutrition. Libre 2 compared with finger-prick tests.

Glucose tools

See it all from your export

The free CGM report reads the whole file: your 24-hour profile (AGP), time in range, GMI, variability, your biggest rises and overnight sensor pressure.

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Questions people ask

How do I calculate GMI from my CGM average?
Multiply your average glucose in mg/dL by 0.02392 and add 3.31. With mmol/L, multiply by 0.43056 and add 3.31. An average of 120 mg/dL (6.7 mmol/L) gives a GMI of 6.2%. Use at least 14 days of sensor data.
Is GMI the same as HbA1c?
No. HbA1c is measured in a blood sample; GMI is an estimate of it from the sensor’s average. In the study that made GMI, the two differed by half a point or more in 28% of people. HbA1c also depends on how long your red blood cells live, and the sensor covers only the weeks you wore it.
What is the difference between GMI and eAG?
They are the same relationship seen from opposite ends. eAG (estimated average glucose) starts from a lab HbA1c and estimates the average glucose that usually goes with it (ADAG study, 2008). GMI starts from a CGM average and estimates the A1C. They come from different studies, so going there and back doesn’t give exactly the same number.
Why is my GMI different from my lab A1C?
Common reasons: the sensor covered different weeks from the ones the blood test reflects, your red blood cells live longer or shorter than average, iron deficiency or anaemia, or the sensor reads a little high or low. Consumer sensors can read high: in one study a Libre 2 read about 0.9 mmol/L (16 mg/dL) above finger-prick tests (Hutchins et al. 2025).

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Information, not a diagnosis. HealthOS is a wellness product, not a medical device: these numbers can’t tell you whether anything needs treatment. Talk to a doctor about your results.