An A1C of 6.5% or higher is the threshold for a diabetes diagnosis, and the higher it climbs above that, the greater the risk to your health. But “bad” is relative. An A1C of 5.7% to 6.4% already signals prediabetes, meaning blood sugar has been running higher than normal for months. To understand what your number means, you need to know where it falls on the scale and what that translates to in daily blood sugar terms.
What A1C Actually Measures
A1C reflects your average blood sugar over roughly the past two to three months. It works by measuring how much glucose has attached to hemoglobin, the protein in red blood cells that carries oxygen. Because red blood cells live about 90 to 120 days, the test captures a rolling average rather than a single snapshot. This makes it more useful than a fasting glucose reading for understanding long-term blood sugar control.
You can convert any A1C percentage into an estimated average glucose (eAG) in mg/dL using a simple formula: multiply the A1C by 28.7, then subtract 46.7. So an A1C of 7% means your blood sugar averaged about 154 mg/dL over the past few months. At 9%, that average jumps to around 212 mg/dL. At 10%, it’s roughly 240 mg/dL.
The Key A1C Ranges
Here’s how the numbers break down:
- Below 5.7%: Normal. Average blood sugar is around 117 mg/dL or lower.
- 5.7% to 6.4%: Prediabetes. Blood sugar is elevated enough to cause gradual damage, and without changes, many people in this range progress to type 2 diabetes.
- 6.5% or higher: Diabetes. This is the diagnostic cutoff used by most major medical organizations.
Within the diabetes range, numbers vary enormously. Someone with well-managed type 2 diabetes might sit at 6.8%. Someone who hasn’t been diagnosed yet, or whose treatment isn’t working well, could be at 10% or above. The higher the number, the more urgently it needs to come down.
Where Complications Start
The risk of serious complications doesn’t wait for your A1C to reach extreme levels. Research published by the American Diabetes Association found that the risk of microvascular complications, which include vision damage, kidney disease, and amputations, increases significantly once A1C reaches 7.2%. At that level, the risk was about 32% higher compared to people with A1C in the mid-6% range. At 8.1% to 8.5%, the risk was roughly 48% higher. By the time A1C climbed above 9.5%, the risk was 64% higher.
This matters because these complications develop silently. High blood sugar damages the small blood vessels that supply your eyes, kidneys, and nerves long before you feel symptoms. By the time you notice vision changes or numbness in your feet, the damage is already well underway. That’s why the number on the lab report is so important: it’s an early warning system for problems you can’t yet feel.
What Doctors Generally Aim For
The American Diabetes Association’s 2025 guidelines recommend an A1C target below 7% for most non-pregnant adults with diabetes. That corresponds to an average blood sugar of about 154 mg/dL. Some people can safely aim lower, down to 6.5% or even close to normal, if they can get there without frequent episodes of dangerously low blood sugar (hypoglycemia).
Not everyone benefits from aggressive targets, though. For older adults, especially those who are frail or have other significant health conditions, a slightly higher A1C may be more appropriate. Pushing blood sugar too low can cause dizziness, confusion, falls, and even heart problems. The American Geriatrics Society recommends individualizing goals for older adults, with 7% or below being reasonable for those in good health and higher targets making sense for people with limited life expectancy or complex medical situations.
What Your Number Means in Practical Terms
Here’s a quick reference for converting A1C to the average blood sugar your body has been running:
- 6%: ~126 mg/dL
- 6.5%: ~140 mg/dL
- 7%: ~154 mg/dL
- 7.5%: ~169 mg/dL
- 8%: ~183 mg/dL
- 8.5%: ~197 mg/dL
- 9%: ~212 mg/dL
- 10%: ~240 mg/dL
If you’ve been checking your blood sugar at home with a finger-stick meter, these numbers should look familiar. An A1C of 8% means your blood sugar has been averaging in the low 180s, which is consistently above the 140 mg/dL mark where damage to blood vessels accelerates. An A1C of 10% means your average has been hovering around 240 mg/dL, a level that puts sustained strain on nearly every organ system.
When A1C Gets Dangerously High
An A1C above 9% is often considered poorly controlled diabetes, and above 10% signals a serious problem that needs immediate attention. At these levels, blood sugar spikes can reach 300 mg/dL or higher on a regular basis. Sustained blood sugar above 300 mg/dL raises the risk of diabetic ketoacidosis (DKA), a medical emergency most common in type 1 diabetes but possible in type 2 as well.
Warning signs of a blood sugar crisis include extreme thirst, frequent urination, nausea and vomiting, belly pain, weakness, shortness of breath, fruity-smelling breath, and confusion. These symptoms can develop over hours to days. If your blood sugar reads above 300 mg/dL on more than one test, or if you have high ketone levels in your urine, that’s an emergency situation.
People with very high A1C numbers who haven’t been diagnosed yet sometimes experience these symptoms and assume they have the flu or food poisoning. If the symptoms keep recurring or don’t resolve, checking blood sugar is a critical step.
When the Test Itself Can Be Wrong
A1C is reliable for most people, but certain conditions can push the result artificially high or low. According to the CDC, factors that can distort your A1C include severe anemia, kidney failure, liver disease, blood disorders such as sickle cell disease or thalassemia, certain medications (including opioids and some HIV drugs), recent blood loss or transfusions, and early or late pregnancy.
If you have any of these conditions, your A1C may not accurately reflect your actual blood sugar control. In those situations, your doctor may rely more heavily on direct blood sugar measurements, like fasting glucose or a glucose tolerance test, to get an accurate picture. This is especially important for people of African, Mediterranean, or Southeast Asian descent, who are more likely to carry hemoglobin variants that affect the test.
Lowering a High A1C
The good news is that A1C responds to changes. Because it reflects a two-to-three-month average, you can see meaningful improvement within one testing cycle if you make sustained changes. Dropping A1C by even 1% significantly reduces the risk of complications.
The most impactful changes are the ones that lower your blood sugar after meals: reducing refined carbohydrates, increasing physical activity (even walking after meals makes a measurable difference), losing 5% to 7% of your body weight if you’re overweight, and taking medications consistently if they’ve been prescribed. For people in the prediabetes range, these lifestyle changes alone can prevent or delay progression to diabetes.
A1C is typically rechecked every three months when blood sugar is above goal, and every six months once it’s stable. Each recheck gives you a clear measure of whether what you’re doing is working. If your number isn’t budging despite real effort, that’s useful information too, because it usually means your treatment plan needs to be adjusted rather than that you’re doing something wrong.