Average Blood Sugar (A1C) Calculator

Type the percentage from your lab report into the A1C field. The field accepts 4% to 15% in steps of 0.1. Enter 7.

The headline result reads 154 mg/dL, the 154.2 from the formula rounded to a whole number. Below it you get 8.6 mmol/L and the reference category Diabetes range.

That category label needs care. It is the American Diabetes Association's diagnostic band, and the calculator shows it for every A1C of 6.5% or higher, whatever the reason for the test. For someone already diagnosed, a 7% result is not a new finding. The ADA Standards of Care suggest an A1C goal below 7% for many non-pregnant adults with diabetes, with individual goals set higher or lower by a clinician.

Next, compare the eAG with your own glucose data. If your meter or CGM averages around 150 mg/dL, it agrees with a 7% A1C. If it averages 120 or 190, that is still inside the ADAG range of 123–185 mg/dL, or close to it, and it happens often. A gap much wider than that is worth raising with your care team.

Estimated average glucose: eAG (mg/dL) = 28.7 × A1C − 46.7, where A1C is the percentage reported by an NGSP-certified laboratory method. Each full percentage point of A1C adds 28.7 mg/dL, or about 1.59 mmol/L, to the estimate.

Unit conversion: eAG (mmol/L) = eAG (mg/dL) ÷ 18.0182, the conversion factor for glucose based on its molar mass. The results panel shows mg/dL as a whole number and mmol/L to one decimal place.

Reference category (ADA Standards of Care, Section 2): below 5.7% is Normal range; 5.7% up to but not including 6.5% is Prediabetes range; 6.5% and above is Diabetes range.

Where the equation came from: the ADAG study followed 507 adults at 10 international centres, including people with type 1 diabetes, type 2 diabetes and no diabetes. Average glucose over the previous three months was measured with continuous glucose monitoring and frequent fingerstick testing, then compared with a centrally measured A1C. A straight line fitted the data with an R² of 0.84, which means A1C explains most, but not all, of the difference in average glucose between people.

A note on rounding: at exactly 6% the formula gives 125.5 mg/dL, and the results panel displays 125 because of how the computer stores that decimal. Published ADAG tables round the same value to 126. Neither is more correct; the difference is one digit of rounding.

Enter 9. The eAG is 211.6 mg/dL (11.7 mmol/L), displayed as 212 mg/dL, and the ADAG 95% range is 170–249 mg/dL.

Compared with 7%, that is 57.4 mg/dL higher. The formula is a straight line, so every one-point change moves the estimate by the same 28.7 mg/dL wherever you start. Going from 9% to 8% lowers the estimate by as much as going from 8% to 7% does.

The two diagnostic boundaries translate the same way. The prediabetes threshold of 5.7% corresponds to about 117 mg/dL (6.5 mmol/L). The diabetes threshold of 6.5% corresponds to about 140 mg/dL (7.8 mmol/L). An average of 140 mg/dL around the clock may not sound high, but it is an average over nights, fasting hours and meals, not a post-meal reading.

The ranges also get wider as A1C rises: 62 mg/dL across at 7% and 79 mg/dL across at 9%. A higher A1C gives a less precise estimate of any one person's true average.

A1C measures glucose attached to hemoglobin, so it depends on how long red blood cells survive. The ADA Standards of Care (Section 2) list conditions that change the link between A1C and glucose. These include some hemoglobin variants, pregnancy, glucose-6-phosphate dehydrogenase (G6PD) deficiency, HIV, and anything that changes red cell turnover, such as anemia, recent blood loss or transfusion, and chronic kidney disease. In those situations the ADA recommends plasma glucose tests, not A1C, for diagnosing diabetes.

The direction of the error depends on the cause. When red cells are replaced faster than normal, they have less time to collect glucose and A1C reads falsely low. That happens after bleeding or transfusion, with hemolysis, and during treatment with erythropoietin. Iron-deficiency anemia, by contrast, has been associated with falsely high readings. Advanced kidney disease can push A1C either way.

Pregnancy lowers A1C because red cell turnover rises, which is one reason the ADA sets a tighter pregnancy goal of below 6% when it can be reached without significant hypoglycemia. People with homozygous hemoglobin variants such as sickle cell disease (HbSS) have no normal hemoglobin A, so A1C cannot be measured at all. Most assays used in the U.S. are accurate for people carrying one copy of a common variant, but not every method is.

In any of these cases the calculator's eAG inherits the distortion. Fructosamine, glycated albumin or continuous glucose monitoring may give a truer picture, and a clinician can decide which fits.

The ADAG equation was also built from non-pregnant adults aged 18 to 70, with people who had significant kidney disease or anemia excluded.

This calculator is not a diagnostic test and says nothing about whether your diabetes treatment is right. It applies one population equation to one number. Your own relationship between A1C and average glucose can sit anywhere inside the ADAG range, and people with the same A1C can differ by 60 mg/dL or more in true average glucose.

An average hides highs and lows. Two people with identical eAG values can have very different day-to-day patterns: one steady, the other swinging between hypoglycemia and spikes above 250 mg/dL. Only meter or CGM data shows that pattern.

A1C is weighted towards recent weeks rather than spread evenly across three months. The NGSP notes that glucose levels in the preceding 30 days contribute substantially more to the result. A change in treatment a month ago will already be visible.

Do not use the result to adjust insulin or other medication, and do not use it in pregnancy, advanced kidney disease, anemia or known hemoglobin variants without clinical interpretation.

A1C describes the outcome; other tools look at what drives it. The HOMA-IR insulin resistance calculator uses fasting glucose and fasting insulin to estimate how hard the body is working to keep glucose down, which can be abnormal before A1C has risen at all. For the day-to-day side, the meal glycemic load calculator adds up how much a meal's carbohydrate is likely to raise blood glucose, the kind of spike an A1C average smooths over. Diabetes also raises cardiovascular risk. The cholesterol ratio calculator reads a lipid panel, and the Framingham cardiac risk calculator combines diabetes status with cholesterol, blood pressure and smoking into a ten-year estimate.