A good A1c for a non-diabetic person is below 5.7%, which translates to an estimated average blood sugar of about 117 mg/dL or less. This is the threshold used by the CDC and the American Diabetes Association to separate normal blood sugar control from prediabetes. Most healthy adults without diabetes fall somewhere between 4.0% and 5.6%.
What A1c Measures
A1c reflects your average blood sugar over roughly the last two to four months. It works by measuring how much glucose has attached to hemoglobin, the protein in red blood cells that carries oxygen. Since red blood cells live about 120 days, glucose gradually accumulates on them over their lifespan, giving a snapshot of your blood sugar trends rather than a single moment in time.
That said, the test is weighted toward more recent weeks. About 75% of the A1c reading comes from blood sugar levels in the past 30 days, with only about 25% reflecting glucose exposure from 60 to 120 days prior. This means changes you make today will start showing up in your A1c relatively quickly.
The Three A1c Categories
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
Within the prediabetes range, risk isn’t flat. Someone at 6.3% is at significantly higher risk of progressing to type 2 diabetes than someone at 5.8%. If your result lands anywhere in the 5.7% to 6.4% zone, the higher end warrants more attention and more aggressive lifestyle changes.
What Your A1c Means in Everyday Blood Sugar
A1c percentages can feel abstract. Converting them to estimated average glucose (eAG) gives you a number you can compare to a finger-stick reading or continuous glucose monitor. The standard conversion formula is: eAG (mg/dL) = 28.7 × A1c − 46.7. Here’s what that looks like in practice:
- A1c of 5.0%: average blood sugar around 97 mg/dL
- A1c of 5.5%: average blood sugar around 111 mg/dL
- A1c of 6.0%: average blood sugar around 126 mg/dL
- A1c of 6.5%: average blood sugar around 140 mg/dL
These are averages with a fairly wide confidence interval. An A1c of 5.0% corresponds to an average glucose of 97 mg/dL, but the actual range for individuals could be anywhere from 76 to 120 mg/dL. Two people with the same A1c can have different day-to-day glucose patterns.
A1c Naturally Rises With Age
The standard cutoff of 5.7% doesn’t account for age, but A1c does creep upward as you get older, even in people with completely normal glucose tolerance. Data from the Framingham Offspring Study and the national NHANES survey show that A1c increases by about 0.01 percentage points per year in non-diabetic adults. That’s small year to year but adds up over decades.
For adults under 40, the upper limit of normal (97.5th percentile) was 5.6% to 6.0% depending on the study population. For adults 70 and older, that upper limit stretched to 6.2% to 6.6%, all in people confirmed not to have diabetes. This doesn’t mean a reading of 6.2% at age 75 is “fine,” but it does mean that a slight upward drift from your results in your 30s isn’t necessarily a red flag on its own.
When Your A1c Might Not Be Accurate
Several common conditions can push your A1c reading higher or lower than your actual blood sugar levels would suggest. Knowing this matters because a misleading result could trigger unnecessary worry or, worse, false reassurance.
Iron deficiency anemia is one of the most common causes of a falsely elevated A1c. Vitamin B-12 and folate deficiency anemias have the same effect. All of these slow red blood cell turnover, giving glucose more time to attach to hemoglobin. Chronic alcohol use and kidney disease (uremia) can also inflate the number.
On the other side, conditions that speed up red blood cell turnover tend to produce falsely low readings. These include acute or chronic blood loss, hemolytic anemia, an enlarged spleen, and end-stage kidney disease (where chronic anemia shortens red blood cell survival). Certain supplements, particularly vitamin E, can also lower A1c independently of any change in blood sugar.
If you have any of these conditions, your doctor may use other tests, like fasting glucose or an oral glucose tolerance test, to get a more reliable picture.
A1c During Pregnancy
Pregnant women without diabetes tend to run lower A1c values than the general population. In a study of over 4,000 non-diabetic pregnant women, the reference ranges by trimester were 4.0% to 5.5% in the first trimester, 3.9% to 5.3% in the second, and 4.1% to 5.7% in the third. The dip in the second trimester reflects normal physiological changes in blood volume and red blood cell turnover. A1c is not the primary screening tool for gestational diabetes, but these ranges offer useful context if it appears on your prenatal lab work.
Lowering Your A1c Through Lifestyle
If your result is in the prediabetes range, the most effective interventions are the least exotic ones: diet, exercise, and modest weight loss. Losing just 5% to 10% of your body weight can meaningfully lower your A1c. For someone who weighs 200 pounds, that’s 10 to 20 pounds. Research from the Johns Hopkins diabetes prevention program found that lifestyle changes producing this kind of modest weight loss delayed the onset of type 2 diabetes by 34% over four years compared to no intervention.
The dietary approach that consistently works focuses on reducing refined carbohydrates and added sugars, which are the foods that cause the sharpest blood sugar spikes. Replacing them with fiber-rich whole grains, vegetables, lean protein, and healthy fats smooths out glucose levels throughout the day. Regular physical activity, even brisk walking, helps your cells use glucose more efficiently. Because A1c is weighted toward the most recent month, consistent changes can start showing results in your next test, typically ordered three months later.