HbA1c to Glucose Converter

HbA1c measures the fraction of hemoglobin that has glucose attached to it, which accumulates over a red blood cell's roughly three-month lifespan and so reflects average blood glucose over that period rather than a single moment. This calculator converts an HbA1c percentage into an estimated average glucose (eAG) using the linear formula from the ADAG (A1c-Derived Average Glucose) study, published by Nathan and colleagues in Diabetes Care in 2008: eAG (mg/dL) = 28.7 x HbA1c - 46.7. Because the formula is a straight line with a positive slope, raising HbA1c always raises the estimated average glucose across this calculator's full 3-20% input range -- there is no plateau or reversal. The glucose figure is also shown in mmol/L, the unit most labs outside the United States use, by dividing the mg/dL figure by 18.018 (glucose's molecular weight divided by 10).

Alongside the glucose estimate, the calculator classifies the HbA1c itself against the standard American Diabetes Association diagnostic thresholds: below 5.7% is normal, 5.7% to 6.4% is prediabetes, and 6.5% or above is diabetes. An eAG figure is a population-level average, not a substitute for a self-monitored glucose log -- individual patients can have the same HbA1c with very different day-to-day glucose swings, so eAG and finger-stick or continuous glucose readings are meant to be compared, not treated as interchangeable. The formula itself comes from the ADAG (A1c-Derived Average Glucose) study, led by Dr. David Nathan and published in Diabetes Care in 2008, which paired roughly 2,700 glucose readings per subject over three months against measured HbA1c to derive the linear relationship this calculator uses.