A1C calculator: average glucose, eAG and GMI

What this calculator does

It has two modes:

• I have my A1C. It works out the estimated average glucose (eAG) that matches that A1C, using the formula from the ADAG study: eAG (mg/dL) = 28.7 × A1C − 46.7. It also gives your A1C in mmol/mol, the IFCC unit many European labs report.
• I have my sensor's average glucose. It works out the GMI (glucose management indicator), the number sensor reports show: GMI (%) = 3.31 + 0.02392 × average glucose in mg/dL. Next to it you'll see the A1C estimated with the ADAG formula, so you can see they don't always agree.

GMI and A1C are not the same thing

A1C is a blood test: it measures how much hemoglobin has bound to glucose over roughly three months. GMI is a calculation from your sensor readings. It was renamed (it used to be called "estimated A1C") precisely because so many people found their lab result didn't match the number in their app.

It is normal for them to differ. How long your red blood cells live, anemia, pregnancy or some hemoglobin variants all move A1C without your average glucose changing. That's why the two numbers are read together, not one instead of the other.

Quick table

A1C	mmol/mol	Estimated average glucose
6%	42	126 mg/dL · 7.0 mmol/L
7%	53	154 mg/dL · 8.6 mmol/L
8%	64	183 mg/dL · 10.2 mmol/L
9%	75	212 mg/dL · 11.8 mmol/L

Where to see your average glucose and GMI

The Trends tab in Dulce works out your average glucose, GMI and time in range from your FreeStyle Libre readings over 7, 14, 30 or 90 days. We explain it in the Trends guide.

Sources

• Nathan D. M. et al. Translating the A1C Assay Into Estimated Average Glucose Values. Diabetes Care 2008;31:1473-1478. doi.org/10.2337/dc08-0545
• Bergenstal R. M. et al. Glucose Management Indicator (GMI). Diabetes Care 2018;41:2275-2280. doi.org/10.2337/dc18-1581

This article is for information and does not replace advice from your care team. Dulce is not a medical device and does not replace your sensor's alarms.