HbA1c (hemoglobin A1c) measures the percentage of your red blood cells coated with sugar. Because red cells live about 3 months, A1c reflects your average blood sugar over the past 2–3 months — not just the moment of the test.
It's the single most important test for diabetes in the US, where 38 million people have diabetes and 96 million have prediabetes. Unlike a fasting glucose, you don't need to fast for an A1c.
Want to see what your A1c means in everyday blood-sugar numbers? Use our A1c → average glucose calculator.
HbA1c reference ranges (US standard)
These ranges are aligned with Quest Diagnostics and LabCorp. Your own report prints the exact range your lab used — always defer to that range, since methods differ slightly between labs.
| Parameter | Normal Range | What it measures |
|---|---|---|
| HbA1c — Normal | Below 5.7% | Average glucose under ~117 mg/dL |
| HbA1c — Prediabetes | 5.7% – 6.4% | Average glucose ~117–137 mg/dL |
| HbA1c — Diabetes | 6.5% or higher | Average glucose ~140+ mg/dL |
| Treatment target (most adults) | Below 7.0% | Common goal with diabetes (ADA) |
Understanding your A1c
What the categories mean
An A1c below 5.7% is normal. 5.7–6.4% is prediabetes — a warning zone where lifestyle changes can often reverse the trend. 6.5% or higher on two tests means diabetes. Each 1% rise in A1c corresponds to roughly a 29 mg/dL rise in average blood sugar.
Prediabetes is reversible
The 96 million Americans with prediabetes have a real opportunity: studies show that losing 5–7% of body weight and adding regular activity can cut the risk of progressing to diabetes by more than half.
If you already have diabetes
Most adults aim for an A1c below 7%, though targets are personalized — older adults or those with other conditions may have a higher goal. A1c is usually checked every 3–6 months.