A1c Calculator – Hemoglobin A1c to Average Blood Sugar

Hemoglobin A1c measures the percentage of your red blood cells that have glucose-coated hemoglobin attached to them. Because red blood cells live for roughly 90 to 120 days, this metric gives a reliable three-month historical picture of your blood glucose levels. The mathematical relationship between Hemoglobin A1c and average blood sugar is derived from the landmark Diabetes Control and Complications Trial (DCCT). The primary formula used to convert A1c to estimated average blood sugar (eAG) in mg/dL is: Average Blood Sugar = (Hemoglobin A1c × 28.7) - 46.7. You can also rearrange this equation to estimate your A1c if you know your average daily glucose readings.

Imagine you receive a lab report showing a Hemoglobin A1c level of 7.0%. You want to know what average daily blood glucose level corresponds to this percentage. First, substitute 7.0 into our formula. Multiply 7.0 by 28.7, which gives 200.9. Next, subtract 46.7 from 200.9. The resulting value is 154.2. Therefore, an A1c of 7.0% corresponds to an estimated average blood sugar of approximately 154 mg/dL over the past three months.

Keep in mind that eAG is a statistical estimate, not a direct replacement for daily finger-prick checks or continuous glucose monitors (CGMs). Conditions that alter red blood cell turnover, such as anemia, recent blood loss, or certain hemoglobin variants, can make A1c readings less accurate. Always consult your primary care physician or endocrinologist to interpret your lab results within the context of your overall metabolic health profile.