Tool
GMI calculator
Enter the mean (average) glucose from your continuous glucose monitor report. GMI is an A1c-like number estimated from CGM data.
Use a mean from at least 14 days of CGM data, as the GMI authors advise (Bergenstal 2018). Nothing you type leaves this page.
GMI (mmol/mol) = 12.71 + 4.70587 × mean glucose (mmol/L)
What GMI is
GMI was proposed in 2018 to replace the older "estimated A1c" label for CGM-based estimates. It is calculated from the mean glucose of CGM data with a regression formula derived from people who had both CGM data and a lab A1c (Bergenstal 2018).
GMI is not the same as a lab A1c
- A lab A1c measures glucose attached to hemoglobin. GMI is calculated from sensor readings. The two can differ for the same person (Bergenstal 2018).
- A1c is affected by things that change red blood cells, such as blood loss, anemia or kidney failure (NIDDK). GMI is not, which is one reason the two can disagree.
- A finger-stick meter average is not a CGM mean: a few spot checks a day can miss highs and lows. Use the A1c converter to compare a lab A1c with an average glucose instead.
Going the other way
See GMI vs A1c for a side-by-side chart. The A1c converter uses a different formula (ADAG) that turns a lab A1c into estimated average glucose (Nathan 2008). GMI goes from CGM mean glucose to an A1c-like number. The two formulas come from different studies, so converting back and forth between them will not give exactly the same number.
Sources
- Bergenstal RM, Beck RW, Close KL, et al. Glucose Management Indicator (GMI): a new term for estimating A1C from continuous glucose monitoring. Diabetes Care. 2018;41(11):2275-2280. doi.org/10.2337/dc18-1581
- Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ; A1c-Derived Average Glucose (ADAG) Study Group. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008;31(8):1473-1478. doi.org/10.2337/dc08-0545
- National Institute of Diabetes and Digestive and Kidney Diseases (NIH). The A1C Test & Diabetes. www.niddk.nih.gov/health-information/diagnostic-tests/a1c-test
Written and maintained by the controla1clevels.com editorial team. We do not have a medical reviewer; every claim links to its primary source above. Last reviewed: 2026-10-25. Spotted an error? See About.