The A1C test uses three main ranges: below 5.7% is normal, 5.7% to 6.4% indicates prediabetes, and 6.5% or above means diabetes. These cutoffs, established by the CDC and American Diabetes Association, are the standard for diagnosis in adults. But there’s more to understanding your A1C number than just which category it falls into.
How the A1C Test Works
When glucose circulates in your bloodstream, some of it naturally sticks to the hemoglobin inside your red blood cells. This process, called glycation, happens continuously and can’t be reversed once it occurs. Since red blood cells live for roughly 106 days on average, the A1C test captures a weighted snapshot of your blood sugar over the previous two to three months. Higher blood sugar means more glucose attached to hemoglobin, which means a higher A1C percentage.
Unlike a finger-stick glucose reading that only tells you what’s happening right now, A1C reflects the bigger picture. A single high-sugar meal or a stressful morning won’t move it much. It takes weeks of consistently elevated blood sugar to push the number up, which is why it’s useful for both diagnosing diabetes and tracking how well it’s being managed over time.
The Three Diagnostic Ranges
Normal (below 5.7%): Your blood sugar has been well-controlled over the past few months. An A1C of 5.0%, for example, corresponds to an average blood glucose of about 97 mg/dL.
Prediabetes (5.7% to 6.4%): Blood sugar is higher than normal but not yet in the diabetes range. This is a window where lifestyle changes, particularly weight loss, exercise, and dietary shifts, can often prevent or delay progression to type 2 diabetes. About 1 in 3 American adults fall into this range, and many don’t know it.
Diabetes (6.5% or above): At this level, your body is no longer managing blood sugar effectively. Diagnosis typically requires confirmation with a second test on a different day unless symptoms are already present.
What Your A1C Translates to in Daily Blood Sugar
One of the most practical things you can do with an A1C result is convert it to an estimated average glucose (eAG), which tells you roughly what your blood sugar has been running day to day. The formula is straightforward: multiply your A1C by 28.7, then subtract 46.7. The result is your average glucose in mg/dL.
- A1C of 6% = average glucose of about 126 mg/dL
- A1C of 7% = about 154 mg/dL
- A1C of 8% = about 183 mg/dL
- A1C of 9% = about 212 mg/dL
- A1C of 10% = about 240 mg/dL
Each 1% increase in A1C corresponds to roughly a 28–29 mg/dL jump in average blood sugar. If you check your blood sugar at home, comparing your meter readings to your eAG can reveal whether you’re catching your true highs and lows or mostly testing at stable times.
A1C Targets Vary by Age and Health
The diagnostic cutoffs are the same for everyone, but treatment targets for people already diagnosed with diabetes are not one-size-fits-all. The standard goal for most adults with diabetes is below 7%, but this is adjusted based on individual circumstances.
Younger adults with few other health problems and long life expectancies may be given a tighter target of 6.0% to 6.5%. The rationale is that decades of tightly controlled blood sugar significantly reduce the risk of complications affecting the eyes, kidneys, and nerves. For older adults, particularly those with heart disease, kidney problems, or other significant conditions, guidelines suggest a more relaxed target of 7.5% to 8.0%. Pushing too aggressively for a low number in these patients can cause dangerous drops in blood sugar (hypoglycemia) without enough remaining life expectancy for the long-term cardiovascular benefits to materialize.
For women planning pregnancy, the recommended A1C target is below 6.5% before conception. An A1C above 10% poses serious enough risks to both mother and baby that medical teams strongly advise waiting to conceive until the number comes down.
When A1C Results Can Be Misleading
Because the test depends on hemoglobin inside red blood cells, anything that changes your red blood cells can throw off the result, sometimes significantly.
Conditions that shorten red blood cell lifespan, like hemolytic anemia or recent major blood loss, will falsely lower your A1C. The cells haven’t been around long enough to accumulate the normal amount of glucose, so the reading looks better than your actual blood sugar control. On the flip side, iron deficiency anemia tends to push A1C higher than expected, because older red blood cells make up a larger share of the total and they’ve had more time to collect glucose. Iron replacement therapy can bring the number back down even without any change in blood sugar.
Genetic hemoglobin variants also affect accuracy. People with sickle cell trait, hemoglobin C trait, or elevated fetal hemoglobin may get results that don’t reflect their true glucose levels, with the direction and size of the error depending on the specific variant and the lab method used. Chronic kidney disease adds another layer of complexity: patients on dialysis tend to get A1C results that underestimate their actual blood sugar, making alternative markers like glycated albumin more reliable for tracking their control.
If you have any of these conditions, your results should be interpreted with caution. Your doctor may use fructosamine testing or continuous glucose monitoring to get a more accurate picture.
How Often to Get Tested
If your A1C is normal and you have no risk factors for diabetes, periodic screening (typically every three years starting at age 35, or earlier with risk factors like obesity or family history) is generally sufficient. People with prediabetes benefit from annual testing to catch any progression early. For those with diagnosed diabetes, testing every three to six months is typical, with more frequent checks for anyone who recently changed medications or hasn’t yet reached their target.