A1c to average glucose calculator (eAG and GMI)
An A1c of 7% means your blood sugar has averaged about 154 mg/dL over the past few months. That translation, called estimated average glucose or eAG, is what makes an A1c comparable with the numbers on a glucose meter or a CGM. The calculator works in both directions. Start from a lab A1c to get the average glucose, or start from a CGM or meter average to get the A1c it corresponds to.
How A1c becomes an average glucose
The conversion comes from the A1c-Derived Average Glucose (ADAG) study, published in 2008. Researchers gave 507 adults, with and without diabetes, about 2,700 glucose readings each over three months, mostly from continuous monitors, then compared their average glucose with their A1c at the end. The relationship was close to a straight line:
eAG (mg/dL) = 28.7 × A1c − 46.7
eAG (mmol/L) = 1.5944 × A1c − 2.594
The A1c here is in percent. If your report gives A1c in mmol/mol, the IFCC unit used in the UK, Europe, and Australia, the calculator converts it to percent first. The lab unit converter does that conversion on its own.
Going the other way, from an average glucose to an A1c, reverses the same equation. The calculator shows that as “ADAG A1c” next to the GMI, which is covered below.
A1c to eAG table
| A1c (%) | A1c (mmol/mol) | eAG (mg/dL) | eAG (mmol/L) |
|---|---|---|---|
| 5.0 | 31 | 97 | 5.4 |
| 5.5 | 37 | 111 | 6.2 |
| 6.0 | 42 | 126 | 7.0 |
| 6.5 | 48 | 140 | 7.8 |
| 7.0 | 53 | 154 | 8.6 |
| 7.5 | 58 | 169 | 9.4 |
| 8.0 | 64 | 183 | 10.2 |
| 8.5 | 69 | 197 | 11.0 |
| 9.0 | 75 | 212 | 11.8 |
| 9.5 | 80 | 226 | 12.6 |
| 10.0 | 86 | 240 | 13.4 |
| 10.5 | 91 | 255 | 14.1 |
| 11.0 | 97 | 269 | 14.9 |
| 11.5 | 102 | 283 | 15.7 |
| 12.0 | 108 | 298 | 16.5 |
eAG is an estimate with a wide range
The line fit the study group well, but individual people sat well above and below it. The ADAG paper gives the range that covered 95% of participants at each A1c:
| A1c (%) | eAG (mg/dL) | Range (mg/dL) |
|---|---|---|
| 6 | 126 | 100 to 152 |
| 7 | 154 | 123 to 185 |
| 8 | 183 | 147 to 217 |
| 9 | 212 | 170 to 249 |
| 10 | 240 | 193 to 282 |
So two people with the same 7% A1c can have true averages 60 mg/dL apart. The eAG printed on a lab report is the middle of that range, not a measurement of your own average. It is a single calculation from the A1c, so it adds nothing to the A1c itself when you track results over time.
The study also left out groups whose A1c is known to run off: people with anemia, hemoglobin variants that interfere with the test, kidney or liver disease, recent blood loss or transfusion, and pregnancy, along with children and adults over 70.
eAG and GMI are different numbers
If you wear a continuous glucose monitor, its report probably shows a Glucose Management Indicator, or GMI, in percent. It looks like an A1c but works in the opposite direction. eAG starts from a lab A1c and estimates the average glucose. GMI starts from the CGM’s measured average glucose and estimates the A1c you would expect.
GMI comes from a 2018 study by Bergenstal and colleagues, which fitted CGM averages against lab A1c in a separate group of people:
GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL)
The name replaced the older “estimated A1c,” because the sensor figure and the lab A1c often disagree, and calling both “A1c” confused people. Because the two equations come from different studies, they don’t quite invert each other. They agree near 7% and drift apart above and below it. An average of 100 mg/dL gives a GMI of 5.7% but an ADAG A1c of 5.1%, and an average of 212 mg/dL gives a GMI of 8.4% but an ADAG A1c of 9.0%. The calculator shows both when you start from an average glucose. For a CGM average, GMI is the one your diabetes team will recognize.
Why your A1c and your CGM don’t match
A lab A1c and a CGM’s GMI often disagree, and that is expected. In the Bergenstal study, the two were identical only 19% of the time. They differed by 0.3 percentage points or more about half the time, and by 0.5 points or more 28% of the time. The usual reasons:
- Red blood cells live longer or shorter than average. A1c measures how much glucose has stuck to hemoglobin over the life of your red cells. Longer-lived cells collect more, so the same average glucose gives a higher A1c.
- Glucose sticks to hemoglobin at different rates from one person to the next.
- The time windows differ. A CGM report usually covers the last 14 days, the period the international consensus on CGM reports recommends. A1c reflects about three months, weighted toward the most recent weeks. A recent illness, a steroid course, or a new diet moves the CGM figure first.
- Conditions that affect A1c itself, such as iron deficiency, blood loss, or a hemoglobin variant. The A1c tracking post covers these under when A1c can mislead.
The paper suggests watching the gap over time. If your lab A1c runs consistently higher or lower than your GMI, that offset is probably personal and stable, and it is worth knowing when you read either number. A gap that suddenly changes is worth raising with your clinician.
Tracking A1c and average glucose together
The useful comparison isn’t one A1c against one eAG. It is your lab A1c results and your CGM or meter averages on the same timeline, so you can see whether they move together and how far apart they usually sit. How to track your A1c over time covers what counts as a real change and what to record with each result.
A1c and glucose in HealthViewer
HealthViewer is a lab results tracker that runs on your own computer. It imports A1c results from lab report PDFs, MyChart downloads, and direct connections to your health system, and converts results in mmol/mol to percent so they share one chart. A Dexcom Clarity export imports as daily CGM average glucose and time in range, which you can chart next to your A1c in Trends.
Everything stays in an encrypted file on your computer, with no account and no cloud service. Getting Started walks through the first import.
This calculator is general information, not medical advice. eAG and GMI are estimates from population studies and can differ from your own average. Talk to your clinician about your targets and before changing any treatment.