A1C Calculator

How to use this calculator

Choose which way to convert:

• A1C to glucose: enter your A1C percentage from a lab report or home test kit. You’ll get your estimated average glucose (eAG) in mg/dL and mmol/L.
• Glucose to A1C: enter an average glucose over several weeks, such as the 90-day average from a continuous glucose monitor (CGM), in mg/dL or mmol/L. You’ll get the A1C it corresponds to.

Either way you’ll see the result on the American Diabetes Association (ADA) diagnostic scale, your A1C in IFCC units (mmol/mol), the working, and a conversion chart.

The eAG formula

A1C measures the share of hemoglobin in your red blood cells that has glucose attached. Because red blood cells live for a few months, it reflects your average blood sugar over roughly the past 2 to 3 months.

In 2008, the A1C-Derived Average Glucose (ADAG) study, led by David Nathan and published in Diabetes Care, linked A1C to average glucose measured by continuous and finger-stick monitoring in 507 adults with type 1 diabetes, type 2 diabetes or no diabetes. The best-fit line, which explained 84% of the variation (R² = 0.84), is:

To convert to mmol/L, divide mg/dL by 18. To go from average glucose to A1C, the calculator solves the same line the other way: A1C = (eAG + 46.7) ÷ 28.7.

Worked example

Your lab report shows an A1C of 7.0%:

1. eAG = 28.7 × 7.0 − 46.7 = 154 mg/dL
2. In mmol/L: 154.2 ÷ 18 = 8.6 mmol/L
3. In IFCC units: (7.0 − 2.15) ÷ 0.0915 = 53 mmol/mol

Going the other way, a 90-day CGM average of 126 mg/dL corresponds to an A1C of (126 + 46.7) ÷ 28.7 = 6.0%.

A1C to average glucose chart

Each 1-point rise in A1C corresponds to about 29 mg/dL (1.6 mmol/L) more in average glucose.

What the ranges mean

The ADA’s Standards of Care in Diabetes—2026 use these A1C cut points:

A1C is one of several tests the ADA accepts for diagnosis, alongside fasting plasma glucose and the oral glucose tolerance test. Unless blood sugar is unmistakably high, as in a hyperglycemic crisis, a diagnosis needs confirmation, usually from a second abnormal result. A1C in the prediabetes range signals a higher risk of developing type 2 diabetes, and it’s a good reason to talk to your doctor about screening and prevention.

If you already have diabetes, your care team will set an A1C goal for you. Goals are individual, and they depend on things like your age, other health conditions and the risk of low blood sugar.

When A1C can be misleading

A1C depends on your red blood cells, so anything that changes how long they live or how hemoglobin is measured can make it read high or low. The ADA lists:

• Anemia and treatment with erythropoietin
• Pregnancy, when the ADA recommends plasma glucose tests rather than A1C for diagnosis
• Kidney failure and dialysis, cirrhosis and HIV
• Hemoglobin variants, which interfere with some A1C assays, and G6PD deficiency, which can lower A1C

In these situations, or when your A1C doesn’t match your glucose readings, your clinician may use other tests.

A1C versus your CGM average

The ADAG formula describes an average relationship, and individuals scatter around it. Two people with the same average glucose can have A1C values that differ noticeably. For this reason, CGM reports now show a glucose management indicator (GMI), an A1C-like estimate calculated from CGM data, rather than calling it an A1C. If your lab A1C and your CGM’s GMI disagree consistently, tell your care team.

Lowering your A1C

For people with prediabetes or type 2 diabetes, weight loss, regular physical activity and changes to what you eat can all lower A1C, alongside any medication your doctor prescribes. If weight loss is part of your plan, the calorie deficit calculator sets a daily calorie target for a goal date, and the BMI calculator shows the healthy weight range for your height.

Assumptions and limitations

• The conversion uses a population average; your own A1C-to-glucose relationship may differ.
• A home A1C kit can be less precise than a laboratory test.
• The ranges are the ADA’s adult criteria. They aren’t used to diagnose diabetes during pregnancy and don’t apply to every condition listed above.

Sources

• Nathan DM, Kuenen J, Borg R, et al. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008;31(8):1473–1478.
• American Diabetes Association Professional Practice Committee. 2. Diagnosis and classification of diabetes: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1):S27–S49.
• Hoelzel W, Weykamp C, Jeppsson JO, et al. IFCC reference system for measurement of hemoglobin A1c in human blood and the national standardization schemes in the United States, Japan, and Sweden: a method-comparison study. Clin Chem. 2004;50(1):166–174.
• Bergenstal RM, Beck RW, Close KL, et al. Glucose management indicator (GMI): a new term for estimating A1C from continuous glucose monitoring. Diabetes Care. 2018;41(11):2275–2280.

This calculator converts numbers for general information. It can’t diagnose diabetes or prediabetes; only your doctor can do that, using laboratory tests.

Updated November 2026. Results are estimates for educational purposes and depend on the inputs you provide.