A normal A1c is below 5.7%. This number represents your average blood sugar over the past two to three months, expressed as a percentage. An A1c between 5.7% and 6.4% falls into the prediabetes range, and 6.5% or above indicates diabetes.
What A1c Actually Measures
Glucose in your bloodstream naturally sticks to hemoglobin, the protein inside red blood cells that carries oxygen. The more sugar in your blood over time, the more hemoglobin gets coated. Since red blood cells live for about 90 days, measuring how much sugar is attached to them gives a reliable picture of your blood sugar control over the previous two to three months. That’s what makes A1c different from a finger-stick glucose reading, which only captures a single moment.
The Three Ranges
The CDC uses these cutoffs for the A1c test:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
If your result falls in the normal range, you’re not currently showing signs of insulin resistance or chronically elevated blood sugar. A prediabetes result means your blood sugar is higher than ideal but hasn’t crossed the diabetes threshold. It’s a signal that your body is starting to struggle with blood sugar regulation, and lifestyle changes at this stage can often prevent progression to type 2 diabetes.
How A1c Translates to Daily Blood Sugar
Your A1c percentage maps to an estimated average glucose (eAG), which is the number you’d see on a blood sugar meter in mg/dL. A normal A1c range of 4% to 6% corresponds to an average blood sugar between roughly 70 and 126 mg/dL. For people managing diabetes, most guidelines recommend aiming for an A1c below 7%, which translates to an average blood sugar under about 154 mg/dL.
This conversion is useful because it connects a somewhat abstract percentage to the kind of number you’d recognize from a glucose monitor. If your A1c is 5.4%, your blood sugar has been averaging somewhere around 108 mg/dL over the past few months.
When Your A1c Might Not Be Accurate
Because the test depends on hemoglobin inside red blood cells, anything that changes how long your red blood cells survive or alters the structure of hemoglobin can skew results. This matters more than most people realize.
Conditions that shorten red blood cell lifespan, like hemolytic anemia or recovery from significant blood loss, will produce a falsely low A1c. Your red blood cells haven’t been around long enough to accumulate sugar, so the reading looks better than your actual blood sugar control. On the other end, iron deficiency anemia is associated with falsely elevated A1c. This is particularly relevant during late pregnancy, when iron deficiency is common and can push A1c higher even in people without diabetes.
Genetic hemoglobin variants, including sickle cell trait and hemoglobin C trait, can also affect accuracy depending on the specific lab method used. People with sickle cell disease face multiple compounding factors: anemia, faster red cell turnover, and transfusion needs all make A1c unreliable as a long-term marker. Chronic kidney disease, especially in people on dialysis, presents similar challenges. For these patients, alternative tests that measure sugar attached to other blood proteins may give a more accurate picture.
If you have any of these conditions, your doctor may interpret your A1c differently or use additional tests to confirm your blood sugar status.
Racial Differences in A1c Levels
Research has consistently found that Black Americans tend to have higher A1c readings than white Americans at the same actual blood sugar levels. This isn’t a difference in diabetes risk or blood sugar control. It appears to reflect biological variation in how readily glucose attaches to hemoglobin.
A CDC-linked study of over 5,300 participants found that optimal A1c cutoffs for identifying diabetes and prediabetes were consistently higher in Black participants compared to white participants. For example, the best cutoff for distinguishing prediabetes from normal blood sugar was 5.7% in Black participants but 5.5% in white participants. This means the standard 5.7% threshold may flag some Black individuals as prediabetic when their glucose levels are actually normal, while potentially missing early problems in white individuals. Some researchers have called for individualizing A1c interpretation based on these differences, though the standard cutoffs remain the same for everyone in current clinical practice.
How Often to Get Tested
If your A1c comes back normal, the U.S. Preventive Services Task Force suggests retesting every three years is a reasonable approach, though your doctor may adjust that timeline based on your age, weight, family history, and other risk factors. If your result falls in the prediabetes range, the CDC recommends repeating the test every one to two years to track whether your blood sugar is stable, improving, or trending toward diabetes.
People already diagnosed with diabetes typically get tested two to four times per year, depending on how well their blood sugar is controlled and whether their treatment plan has recently changed.
What Moves Your A1c Up or Down
Because A1c reflects a two-to-three-month average, it responds to sustained changes rather than daily fluctuations. The biggest drivers are the same ones that affect blood sugar overall: diet, physical activity, body weight, sleep, and stress. Reducing refined carbohydrates and added sugars, increasing movement, and losing even a modest amount of weight (5% to 7% of body weight) have all been shown to meaningfully lower A1c in people with prediabetes.
It takes roughly two to three months for a lifestyle change to show up clearly in your A1c result. If you’ve made changes and want to see the effect, retesting sooner than eight weeks won’t give you the full picture.