A normal A1C is below 5.7%. This number represents the percentage of your red blood cells that have glucose attached to them, averaged over roughly three months. An A1C between 5.7% and 6.4% falls into the prediabetes range, and 6.5% or higher indicates diabetes.
What the A1C Test 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 about three months before your body replaces them, the A1C test captures a rolling average of your blood sugar levels over that entire window. That makes it more useful than a single finger-stick reading, which only tells you what’s happening right now.
One practical advantage: you don’t need to fast before an A1C test. A standard fasting glucose test requires at least eight hours without eating, and the results can swing based on stress, illness, or even the time of day. A1C sidesteps all of that. A single blood draw at any time gives your doctor a reliable picture of your glucose control over the past 90 days.
A1C Ranges and What They Mean
The three categories are straightforward:
- Normal: Below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
To put those percentages in terms you might recognize from a glucose meter, each A1C level translates to an estimated average blood sugar. An A1C of 5.7% corresponds to an average of about 117 mg/dL. At 6.5%, the diabetes threshold, that average climbs to around 140 mg/dL. An A1C of 7% means an average of roughly 154 mg/dL, and by 9% you’re looking at an average near 212 mg/dL. The conversion formula is simple: multiply the A1C by 28.7 and subtract 46.7 to get estimated average glucose in mg/dL.
How Often to Get Tested
The American Diabetes Association’s 2025 guidelines recommend screening at least every three years if your results come back normal and you don’t have additional risk factors. If your A1C lands in the prediabetes range (5.7% to 6.4%), yearly testing is recommended. More frequent screening may make sense if your weight changes significantly or you develop new risk factors between tests.
For people already diagnosed with diabetes who are managing it with medication or lifestyle changes, doctors typically check A1C two to four times a year to track whether the treatment plan is working.
A1C Targets for People With Diabetes
Normal and target are not the same thing. If you have diabetes, the goal usually isn’t to push your A1C all the way down to 5.6%. For most adults with diabetes, the general target is below 7%. But that number gets adjusted based on age, overall health, and the risk of blood sugar dropping too low.
For healthy older adults with few other medical conditions, guidelines suggest aiming for an A1C below 7.5%. For those managing multiple chronic illnesses or mild cognitive decline, the target relaxes to below 8%. And for frail older adults or those in long-term care, the goal loosens further to below 8.5%, because aggressive blood sugar lowering can cause dangerous episodes of hypoglycemia that pose a greater immediate risk than modestly elevated glucose.
When the Test Can Be Inaccurate
A1C is reliable for most people, but certain conditions throw off the results. Anything that changes how long your red blood cells survive will skew the number. If your red blood cells are being destroyed faster than normal, as in hemolytic anemia or after significant blood loss, your A1C will read falsely low because the cells haven’t been around long enough to accumulate glucose.
Iron deficiency anemia pushes results in the opposite direction, making your A1C falsely high. This matters especially in late pregnancy, when iron deficiency is common and can inflate A1C readings even in women without diabetes. Iron supplementation has been shown to bring those artificially elevated numbers back down.
Kidney disease also complicates things. In people on dialysis, chemical changes to hemoglobin can interfere with the test’s accuracy, and A1C tends to underestimate actual blood sugar levels. For these patients, doctors sometimes use alternative markers to monitor glucose control.
If you have any of these conditions, your doctor may rely more heavily on direct glucose measurements or other blood tests rather than A1C alone.
A1C Compared to Fasting Glucose Tests
Both tests diagnose diabetes, but they measure different things. Fasting glucose captures a single snapshot: your blood sugar after at least eight hours without food. The threshold for diabetes is 126 mg/dL or higher. A1C captures the three-month average.
Fasting glucose is cheaper and more widely available, but it’s less consistent. In one large national survey, only about 70% of people who tested at diabetic levels on their first fasting glucose test still tested at diabetic levels when retested two weeks later. Stress, a bad night of sleep, or a recent illness can all temporarily spike the number. A1C doesn’t have that problem. Its biological variability is much lower, and standardization efforts over the past two decades mean that 93% of U.S. labs now produce A1C results with tight consistency.
The tradeoff is that A1C can miss people whose blood sugar spikes sharply after meals but returns to normal between them. That’s why some doctors use both tests together, especially when results are borderline or when one test doesn’t match how a patient is feeling.