A1C Calculator

What A1C measures

The A1C test (also called HbA1c) shows your average blood sugar over the past two to three months. It works by measuring the percentage of your hemoglobin — the oxygen-carrying protein in red blood cells — that has glucose attached. The higher your average blood sugar, the more glucose binds to hemoglobin, so a higher A1C percentage means higher average glucose.

A1C and estimated average glucose (eAG)

Because A1C is a percentage, it can be hard to relate to the day-to-day glucose numbers you see on a meter. The estimated average glucose (eAG) converts A1C into the same units as a glucose reading using the formula from the ADAG study: eAG (mg/dL) = 28.7 × A1C − 46.7. This calculator also shows the result in mmol/L, the unit used in much of the world.

What the numbers mean

• Below 5.7% — normal.
• 5.7% to 6.4% — prediabetes; higher risk of developing diabetes.
• 6.5% or higher — in the diabetes range (a diagnosis is confirmed by your doctor, often with repeat testing).

For many people already diagnosed with diabetes, a common target is below 7%, but individual goals vary — your doctor sets the right target for you.

FAQ

Is eAG the same as a single glucose reading?

No. A finger-stick or meter reading is your glucose at that moment, which rises and falls through the day. The eAG is the long-term average those readings work out to over two to three months.

Can anything throw off an A1C result?

Yes. Conditions affecting red blood cells — such as anemia, recent blood loss, pregnancy, or certain hemoglobin variants — can make A1C read higher or lower than your true average. Your doctor interprets the result in context.

Does this replace medical advice?

No. This tool is for education and converting units only. Always discuss your A1C and what it means for you with a healthcare professional.