A normal A1C is below 5.7%. This number represents the percentage of your red blood cells that have glucose (sugar) attached to them, averaged over the past two to three months. An A1C between 5.7% and 6.4% falls in the prediabetes range, and 6.5% or higher indicates diabetes.
What A1C Actually Measures
When sugar circulates in your bloodstream, some of it 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. An A1C test measures the percentage of red blood cells with this sugar coating.
The reason A1C reflects a two-to-three-month window is straightforward: red blood cells live about three months. So at any given time, your blood contains cells of different ages, each carrying a record of blood sugar levels from the time they were created. The test captures that full history rather than a single snapshot.
The Three A1C Ranges
- Normal: Below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
Within the prediabetes range, risk isn’t flat. Someone at 6.3% is at significantly greater risk of developing type 2 diabetes than someone at 5.8%. If your result comes back in this zone, the specific number matters.
A diabetes diagnosis typically requires the test to be repeated on a second day for confirmation, unless your blood sugar is very high or you already have classic symptoms like excessive thirst, frequent urination, and unexplained weight loss.
A1C Translated to Daily Blood Sugar
If you also check blood sugar with a glucose meter, it helps to know what your A1C means in everyday numbers. The conversion isn’t exact, but a well-established formula translates A1C into an estimated average glucose in mg/dL.
- A1C 5.4% = roughly 108 mg/dL average
- A1C 5.7% = roughly 117 mg/dL average
- A1C 6.0% = roughly 125 mg/dL average
- A1C 6.5% = roughly 140 mg/dL average
- A1C 7.0% = roughly 154 mg/dL average
- A1C 8.0% = roughly 183 mg/dL average
Keep in mind these are averages. Two people with the same A1C could have very different daily patterns. One might have steady blood sugar around 154 mg/dL, while another swings between 80 and 230 and lands at the same average.
Why A1C Can Sometimes Be Inaccurate
Several conditions can push your A1C result higher or lower than your actual blood sugar would suggest. Severe anemia, kidney failure, liver disease, and blood disorders like sickle cell anemia or thalassemia all interfere with the test. So can blood transfusions, significant blood loss, certain medications (including some opioids and HIV drugs), and pregnancy.
If you have any of these conditions, your doctor may rely more heavily on other blood sugar tests for an accurate picture. The two most common alternatives are fasting blood glucose (a single blood draw after at least eight hours without eating) and an oral glucose tolerance test. Fasting glucose below 100 mg/dL is considered normal, while 126 mg/dL or higher indicates diabetes.
How A1C Compares to Fasting Glucose Tests
The biggest practical advantage of A1C is convenience. You don’t need to fast or drink anything beforehand, so it can be done at any time of day during a routine visit. Fasting glucose, by contrast, requires at least eight hours without food, which is why it’s usually scheduled first thing in the morning.
A1C also gives a longer-term view. A fasting glucose test captures a single moment. If you happened to eat unusually well the night before, your fasting number could look reassuringly normal even if your blood sugar has been running high for months. A1C averages out those fluctuations. On the other hand, if you have a condition that distorts A1C results, fasting glucose gives a more reliable reading.
How Often to Get Tested
If you already have diabetes and are meeting your blood sugar goals, testing every six months is typical. If your treatment has recently changed or you’re struggling to reach your targets, every three months is more appropriate.
For people without diabetes, screening guidelines generally recommend starting at age 35 for adults at average risk, or earlier if you have risk factors like being overweight, having a family history of diabetes, or belonging to a racial or ethnic group with higher diabetes rates (including Black, Hispanic, Native American, and Asian American populations).
A1C Targets for Older Adults
The threshold for diagnosing diabetes doesn’t change with age, but treatment targets do. For older adults already managing diabetes, a strict A1C below 7% isn’t always the goal. Pushing blood sugar too low carries its own risks, especially hypoglycemia (dangerously low blood sugar), which can cause falls, confusion, and hospitalization in older people.
For healthy older adults with few other medical issues, an A1C target below 7.5% is generally recommended. For those managing multiple chronic conditions or living with mild to moderate cognitive decline, a target below 8% is more realistic and safer. For frail older adults or those in long-term care, the target may be relaxed further to below 8.5%, with the focus shifting to preventing symptoms rather than hitting a specific number.
These adjusted targets reflect a practical reality: the long-term benefits of tight blood sugar control take years to materialize, while the risks of low blood sugar are immediate. For someone in their 80s with several health conditions, avoiding a hypoglycemic episode today matters more than preventing a complication a decade from now.