A normal HbA1c level is below 5.7%. This percentage reflects your average blood sugar over the past two to three months, making it one of the most reliable snapshots of long-term blood sugar control. Results between 5.7% and 6.4% indicate prediabetes, and 6.5% or higher meets the threshold for a diabetes diagnosis.
What HbA1c Actually Measures
Hemoglobin is the protein inside red blood cells that carries oxygen. When glucose circulates in your bloodstream, some of it naturally attaches to hemoglobin through a chemical bonding process. The more glucose in your blood over time, the more hemoglobin gets coated. An HbA1c test measures the percentage of your hemoglobin that has glucose stuck to it.
Because red blood cells live about 120 days, the test captures a weighted average of your blood sugar over that window. It’s not an even average, though. Roughly half of the glycation reflected in your result happened in the most recent 30 days. Another 40% comes from days 31 through 90, and only about 10% from beyond 90 days. That means your recent weeks matter most. If you made significant dietary changes a month ago, your next A1c will already start to reflect that shift.
The Three Ranges and What They Mean
The cutoffs are straightforward:
- Below 5.7%: Normal. Your body is managing blood sugar effectively.
- 5.7% to 6.4%: Prediabetes. Blood sugar is higher than normal but not yet in the diabetes range. This is the window where lifestyle changes have the biggest impact.
- 6.5% or above: Diabetes. A second test is typically done to confirm the diagnosis.
To put these percentages in more concrete terms, you can convert A1c to an estimated average glucose (eAG) using the formula: multiply your A1c by 28.7, then subtract 46.7. An A1c of 6.0% corresponds to an average blood sugar of about 126 mg/dL. At 6.5%, that average climbs to roughly 140 mg/dL, and at 7.0% it’s around 154 mg/dL. These numbers help bridge the gap between the percentage on your lab report and the glucose readings you might see on a home meter.
When to Get Tested
Current guidelines from the U.S. Preventive Services Task Force and the American Diabetes Association recommend screening for prediabetes and type 2 diabetes starting at age 35 for adults without symptoms. If your result comes back normal, repeat testing every three years is the standard recommendation. Your doctor may suggest earlier or more frequent testing if you have risk factors like obesity, a family history of diabetes, or a history of gestational diabetes.
Conditions That Skew Your Results
An HbA1c test assumes your red blood cells have a normal lifespan and behave in a typical way. Several conditions can throw off the result, sometimes significantly.
Anything that shortens red blood cell survival, like hemolytic anemia or recovery from major blood loss, will falsely lower your A1c. The red blood cells simply haven’t been around long enough to accumulate a representative amount of glucose. On the other hand, iron deficiency anemia pushes A1c readings higher than your actual blood sugar would suggest. This is especially relevant during late pregnancy, when iron deficiency is common and can inflate A1c even in women without diabetes.
Genetic hemoglobin variants, including sickle cell trait and hemoglobin C trait, can also interfere with certain testing methods. People with sickle cell disease face a double challenge: both the hemoglobin variant itself and the rapid red blood cell turnover that comes with it make A1c unreliable as a marker. Chronic kidney disease, particularly in patients on dialysis, tends to cause A1c to underestimate true blood sugar levels. In all of these situations, direct blood glucose monitoring or alternative markers like glycated albumin provide a more accurate picture.
How Exercise and Diet Affect Your A1c
Lifestyle changes produce measurable drops in A1c, and the research on exercise is particularly specific. A large analysis of 158 studies involving over 17,000 people with type 2 diabetes found that all forms of exercise lowered A1c compared to no intervention. High-intensity interval training and combined aerobic-plus-resistance training each reduced A1c by about 0.6 percentage points. Straight aerobic exercise (walking, cycling, swimming) showed a similar reduction. Resistance training alone lowered A1c by about 0.4 points, and even just receiving physical activity advice without a structured program brought a 0.35-point drop.
A 0.5 to 0.6 percentage point reduction might sound small, but in practical terms it can be the difference between a prediabetes reading and a normal one, or between needing medication and managing diabetes through lifestyle alone. These reductions came from regular exercise over weeks to months, not from a single workout. The effects compound with dietary changes, particularly reducing refined carbohydrates and added sugars, and with weight loss when relevant.
A1c in Children and Adolescents
The normal range (below 5.7%) applies to children and adults alike for screening purposes. Where things differ is in treatment targets for children who already have diabetes. For years, guidelines gave kids slightly more lenient A1c goals because aggressive blood sugar lowering carried a higher risk of dangerous low blood sugar episodes in younger patients. That thinking has shifted as better monitoring tools have become available. The American Diabetes Association now recommends children with diabetes stay below 7.5%, while international guidelines from NICE and the International Society for Pediatric and Adolescent Diabetes set even tighter targets of 6.5% and 7.0%, respectively.
What a Borderline Result Means in Practice
If your A1c comes back between 5.7% and 6.4%, you’re in the prediabetes range. About 98 million American adults fall into this category, and most don’t know it. Prediabetes doesn’t inevitably progress to diabetes. It’s a signal that your body is starting to struggle with blood sugar regulation, and it responds well to intervention.
Because recent weeks weigh more heavily in your A1c reading, changes you make now will show up relatively quickly on your next test. A combination of regular physical activity, dietary adjustments, and modest weight loss (if applicable) can pull an A1c back into the normal range within three to six months. If your result is at the higher end of the prediabetes range, close to 6.4%, your doctor may retest sooner than the standard three-year interval to track your trajectory.