A normal hemoglobin A1C level is below 5.7%. This number represents the percentage of your red blood cells that have sugar attached to them, averaged over roughly the past three months. An A1C between 5.7% and 6.4% falls into the prediabetes range, and 6.5% or higher on two separate tests indicates diabetes.
What the A1C Test Actually Measures
When sugar enters your bloodstream, it sticks to hemoglobin, the oxygen-carrying protein inside red blood cells. Everyone has some sugar-coated hemoglobin. The more sugar in your blood over time, the higher the percentage of coated cells.
Red blood cells live for about three months before your body replaces them. That turnover is what makes the A1C test so useful: instead of capturing a single moment (like a finger-stick glucose reading), it reflects your average blood sugar over the entire lifespan of those cells. You don’t need to fast before the test, which makes it more convenient than a fasting glucose draw.
The Three A1C Ranges
Doctors use three straightforward categories:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
A result in the prediabetes range means your blood sugar is elevated but not yet at the diabetes threshold. About 1 in 3 American adults fall into this category, and many don’t know it. The good news is that prediabetes is often reversible with changes to diet, exercise, and weight.
Converting A1C to Average Blood Sugar
A percentage can feel abstract. You can translate your A1C into an estimated average glucose (eAG) in mg/dL using the formula: multiply your A1C by 28.7, then subtract 46.7. Here are some common conversions:
- 5.7% A1C: approximately 117 mg/dL
- 6% A1C: 126 mg/dL
- 6.5% A1C: 140 mg/dL
- 7% A1C: 154 mg/dL
- 8% A1C: 183 mg/dL
- 9% A1C: 212 mg/dL
- 10% A1C: 240 mg/dL
If you check your blood sugar at home with a glucose meter, these eAG numbers give you a sense of how your daily readings line up with your A1C result. Keep in mind that the A1C is a weighted average, so more recent weeks contribute slightly more than earlier ones.
A1C Targets for Older Adults
The standard 5.7% “normal” cutoff applies to healthy adults of any age who don’t have diabetes. But for older adults who already have diabetes, treatment targets are often more relaxed than the under-7% goal typically set for younger patients.
The American Diabetes Association’s framework suggests a target below 7.5% for healthy older adults with few other medical conditions and intact cognitive function. For those managing multiple chronic illnesses or some cognitive decline, a target below 8% is considered reasonable. And for people in poor overall health, long-term care, or end-stage illness, the target may stretch to below 8.5%, because pushing blood sugar too low in these groups carries real risks of falls, confusion, and dangerously low blood sugar episodes. The American College of Physicians goes further, recommending that clinicians avoid targeting a specific A1C at all for patients over 80 or those with limited life expectancy, since the harms of aggressive treatment outweigh the benefits.
Conditions That Skew A1C Results
Because the test depends on hemoglobin and red blood cell lifespan, anything that changes either one can throw off your result. This is worth knowing if your A1C doesn’t seem to match your day-to-day glucose readings.
Conditions that shorten how long red blood cells survive, such as hemolytic anemia or recovery from significant blood loss, will make your A1C appear falsely low. Your red blood cells simply haven’t been around long enough to accumulate sugar at a rate that reflects your true average. On the other hand, iron deficiency anemia is associated with a falsely high A1C, even in people without diabetes. Iron deficiency is especially common in pregnancy, which is why A1C readings taken in late pregnancy may overestimate blood sugar levels.
Kidney disease also complicates things. In patients on dialysis, A1C tends to underestimate actual blood sugar control. For these patients, doctors may rely on alternative markers like glycated albumin instead.
How Hemoglobin Variants Affect Accuracy
The A1C test is designed around hemoglobin A, the most common form of the protein. But millions of people carry hemoglobin variants inherited from their parents, and some of these can produce falsely high or falsely low A1C results depending on the lab method used.
The most common variants that interfere with testing are hemoglobin S (the gene involved in sickle cell trait, most common in African Americans and Hispanic Americans), hemoglobin C (most common in people of West African descent), and hemoglobin E (most common in Southeast Asian Americans). Hemoglobin D and elevated fetal hemoglobin can also affect results. Having one of these variants does not increase your risk of diabetes, but it can mean your A1C result doesn’t accurately reflect your blood sugar. If your heritage traces to Africa, South or Southeast Asia, the Mediterranean, or South and Central America, it’s worth mentioning this to your doctor so the right test method is used or an alternative test is ordered.
How Often to Get Tested
Since the test captures a roughly three-month window, testing more frequently than that doesn’t add much useful information. For people without diabetes whose previous results were normal, an A1C test every three years is a common screening interval starting at age 35, or earlier if you have risk factors like obesity, a family history of diabetes, or a history of gestational diabetes. If your result lands in the prediabetes range, annual testing helps you track whether lifestyle changes are keeping your numbers stable or improving. People with diagnosed diabetes typically get tested two to four times per year, with more frequent checks during periods when treatment is being adjusted.