How the Estimated Average Glucose (eAG) Formula Works
HbA1c (glycated hemoglobin) reports the percentage of hemoglobin in your blood that has glucose attached to it, reflecting your average blood sugar over roughly the prior 2-3 months. Because home glucose meters and continuous glucose monitors report results in mg/dL or mmol/L instead of a percentage, the A1c-Derived Average Glucose (ADAG) Study Group published a formula in 2008 to translate an HbA1c value into an estimated average glucose (eAG) in those same familiar units: eAG (mg/dL) = 28.7 × A1C(%) − 46.7. This calculator applies that formula and also reports the mmol/L equivalent.
Where the formula comes from
The ADAG study linked HbA1c measurements from over 500 participants (with and without diabetes) to frequent self-monitored and continuous glucose readings taken over the same period, then fit a linear regression between the two. The result, eAG (mg/dL) = 28.7 × A1C − 46.7, is the formula endorsed by the American Diabetes Association (ADA) and used on standard HbA1c-to-eAG conversion tables. To convert the mg/dL result to mmol/L, divide by 18.0182 (the same conversion used for any blood glucose value), which is algebraically equivalent to eAG (mmol/L) ≈ 1.59 × A1C(%) − 2.59.
Interpreting your HbA1c category
Alongside the eAG conversion, this calculator classifies the entered A1C using standard ADA diagnostic thresholds: below 5.7% is considered normal, 5.7%-6.4% is prediabetes, and 6.5% or higher is used (typically with a confirmatory repeat test) to diagnose diabetes. It also shows how far the calculated eAG sits from 154 mg/dL (8.6 mmol/L) — the eAG equivalent of a 7% A1C, a treatment target commonly cited by the ADA for many (but not all) adults with diabetes, since individualized goals can range roughly from 6.5% to 8% or higher depending on age, comorbidities, and hypoglycemia risk.
What eAG does not tell you
- eAG is a single average over months — it cannot show how much your glucose swings between highs and lows during the day, which is where meter or CGM data adds value.
- Conditions that shorten or lengthen red blood cell lifespan (certain anemias, kidney disease, pregnancy, recent blood loss or transfusion) can make HbA1c — and therefore the derived eAG — inaccurate.
- Personal A1C treatment goals are individualized by a clinician; the 7%/154 mg/dL comparison shown here is a common reference point, not a personal prescription.
This calculator is intended for educational and informational use only and is not a substitute for professional medical advice, diagnosis, or treatment. Always discuss your HbA1c results and glucose targets with a qualified healthcare provider.