A normal A1C reading is below 5.7%. This number represents the percentage of your red blood cells that have glucose attached to them, giving you and your doctor a snapshot of your average blood sugar over the past two to three months. A result between 5.7% and 6.4% falls into the prediabetes range, and 6.5% or higher indicates diabetes.
What the A1C Test Actually Measures
Glucose in your bloodstream naturally sticks to hemoglobin, the protein inside red blood cells that carries oxygen. The more sugar circulating in your blood over time, the more hemoglobin gets coated. Since red blood cells live for about 120 days, the A1C test captures a weighted average of your blood sugar across that window rather than a single moment.
Not all of that window counts equally, though. Roughly half of the glucose buildup reflected in your A1C happened in the most recent 30 days. Another 40% comes from the period between 31 and 90 days prior, and only about 10% reflects anything beyond 90 days. That means recent changes in your diet or activity level can shift your next result more than you might expect.
A1C Ranges and What They Mean
The CDC uses three straightforward categories:
- Below 5.7%: Normal. Your blood sugar regulation is working well.
- 5.7% to 6.4%: Prediabetes. Your blood sugar is higher than ideal but not yet in the diabetes range. Lifestyle changes at this stage can often prevent progression.
- 6.5% or above: Diabetes. This threshold is typically confirmed with a repeat test on a separate day.
These cutoffs apply to the general adult population. For people already diagnosed with diabetes, target ranges are individualized rather than fixed. Older adults or those with other serious health conditions may have a recommended target as high as 8.0% to 9.0%, while otherwise healthy adults with diabetes often aim for 7.0% or below. The logic is straightforward: pushing blood sugar very low carries its own risks, especially hypoglycemia, so the target balances long-term protection against short-term safety.
Converting A1C to Everyday Blood Sugar Numbers
If you check your blood sugar with a finger stick or continuous monitor, those readings show up in mg/dL. Your A1C percentage translates to an estimated average glucose (eAG) using a simple formula: multiply your A1C by 28.7, then subtract 46.7. Here’s what that looks like in practice:
- A1C of 5.7% (top of normal): roughly 117 mg/dL average
- A1C of 6.0%: about 126 mg/dL average
- A1C of 6.5% (diabetes threshold): about 140 mg/dL average
- A1C of 7.0%: about 154 mg/dL average
Keep in mind this is an average. Two people with identical A1C results can have very different daily patterns. One might have steady blood sugar that hovers near the average, while another swings between high spikes after meals and low dips overnight. The A1C won’t tell you which pattern you have, which is why doctors sometimes pair it with other monitoring.
Why Race and Ethnicity Can Affect Results
A1C doesn’t behave identically across all populations, and this matters enough to be worth understanding. Studies have consistently found that Black Americans tend to have higher A1C readings than white Americans even when their actual blood sugar levels, measured directly, are the same. In one major study (the Diabetes Prevention Program), Black participants had an average A1C of 6.2% compared to 5.8% in white participants despite having comparable fasting glucose and post-meal glucose levels.
The gap isn’t small. A meta-analysis of eleven studies found average differences ranging from 0.2 to 2.0 percentage points, with a typical gap of about 0.65%. The reasons appear to be partly genetic. More than a dozen genetic variants have been linked to A1C levels, and over half of them affect red blood cell biology rather than actual blood sugar. One variant associated with the alpha thalassemia trait is common among people of African descent (roughly 25% carry it) but found in less than 1% of Europeans.
This has real consequences. If a Black patient is held to the same A1C target as a white patient, they may be pushed toward blood sugar levels that are actually lower than intended. Data from one clinical trial showed that an A1C of 7.0% corresponded to an average glucose of about 89 mg/dL in white participants but just 68 mg/dL in Black participants. That 68 mg/dL average is low enough to raise the risk of dangerous hypoglycemia, and a large cardiovascular trial confirmed the pattern: Black participants had a 43% higher risk of hypoglycemia requiring medical assistance compared to white participants, even after adjusting for other factors.
Conditions That Can Skew Your Results
Because the A1C test depends on hemoglobin, anything that changes your red blood cells can throw off the reading. Sickle cell trait, which affects roughly 8% of Black Americans, is one of the most significant. Depending on the lab method used, sickle cell trait can push A1C results falsely high or falsely low. A normal-looking A1C in someone with sickle cell trait doesn’t necessarily mean diabetes is absent.
Other conditions that can distort A1C include iron-deficiency anemia (which tends to raise it), recent blood loss or blood transfusions (which can lower it), kidney disease, and pregnancy. In these situations, doctors may rely on alternative tests, such as fructosamine, which measures glucose-coated proteins over a shorter two-to-three-week window, or direct glucose testing with an oral glucose tolerance test.
How Often to Get Tested
For people with diabetes whose blood sugar is stable and on target, the American Diabetes Association recommends A1C testing at least twice a year. If your treatment has recently changed or you’re not meeting your goals, testing at least every three months is the standard. For people without diabetes, A1C is commonly part of routine screening, especially starting at age 35, or earlier if you have risk factors like obesity, a family history of diabetes, or a history of gestational diabetes.
Because the test is weighted toward recent weeks, timing matters less than you might think. You don’t need to fast before an A1C draw, and time of day doesn’t affect the result. That convenience is one reason it has become the preferred screening tool over fasting glucose tests, which require an overnight fast and can fluctuate based on a single night’s sleep or a stressful morning.