A1C Calculator

A single A1C percentage can be hard to picture in everyday terms, which is where converting it to an estimated average glucose (eAG) helps. This tool moves in both directions: enter an A1C and see the matching eAG in mg/dL or mmol/L, or work backward from a glucose figure to an A1C. Because the result reflects roughly the past two to three months of blood sugar rather than a single morning reading, it offers a steadier view of long-term control and can flag prediabetes earlier. The American Diabetes Association's Standards of Care in Diabetes—2026 keep the familiar cut-offs: an A1C below 5.7% is normal, 5.7% to 6.4% is prediabetes, and 6.5% or higher on two tests is diabetes.

The conversion is the regression from the 2008 A1C-Derived Average Glucose (ADAG) study, which compared lab A1C results with three months of continuous glucose monitoring in 507 adults. To get average glucose in conventional units, the tool applies eAG (mg/dL) = 28.7 × A1C − 46.7, and the mmol/L figure is that result divided by 18. The reverse mode solves the same line for A1C: (glucose + 46.7) ÷ 28.7.

Treat the eAG as an approximation rather than a precise reading. Things like an unusually short or long red blood cell lifespan, anemia, and certain other conditions can pull the real average away from the formula's output. The number this calculator produces is educational and is not a stand-in for a clinician's interpretation or a diagnosis, so bring your actual lab results to your doctor for guidance and any treatment decisions. It also helps to watch how your readings move across several tests, since one isolated value tells you far less than a trend shaped by your habits over time.