A1C Calculator

1. Choose your starting value: A1C percentage (from a blood test) or average blood glucose from a CGM or fingerstick log.
2. Enter the number — typical A1C ranges from 4% to 15%. Glucose ranges from 60 to 400 mg/dL.
3. Read the result — your equivalent average blood glucose appears in both mg/dL (US) and mmol/L (UK/Europe), with classification (normal, prediabetes, diabetes).
4. Use the chart below as a reference for common A1C-to-glucose values and target ranges.

The American Diabetes Association uses the ADAG (A1C-Derived Average Glucose) study formula to convert A1C to estimated average glucose (eAG):

eAG (mg/dL) = 28.7 × A1C − 46.7
eAG (mmol/L) = 1.59 × A1C − 2.59

A1C measures the percentage of hemoglobin molecules bound to glucose. Because red blood cells live ~120 days, A1C reflects average blood sugar over roughly the past 2-3 months.

Example: An A1C of 7.0% converts to 28.7 × 7.0 − 46.7 = 154 mg/dL average glucose. That's the level that, sustained around the clock, would produce a 7.0% A1C.

The American Diabetes Association sets different A1C targets depending on age, comorbidities, and treatment goals. Going too low can be just as dangerous as too high — hypoglycemia kills more diabetics than hyperglycemia in some age groups.

Lowering A1C even modestly produces real benefits. The UKPDS study showed each 1% reduction in A1C cuts microvascular complication risk by ~37%, MI risk by ~14%, and diabetes-related death by ~21%. Most adults can drop A1C 1-2% within 3-6 months through diet, exercise, and medication adjustment.

Track your progress by recalculating after each lab visit. A1C tests are typically ordered every 3-6 months — that matches the lifespan of the red blood cells that A1C measures.