A healthy A1C is below 5.7%. This number represents your average blood sugar over the past two to three months, and it’s the single most common test used to screen for prediabetes and diabetes. An A1C between 5.7% and 6.4% falls into the prediabetes range, while 6.5% or higher indicates diabetes.
What A1C Actually Measures
Sugar 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 115 days on average (roughly three to four months), an A1C test captures a rolling average of your blood sugar rather than a single snapshot.
This is what makes it different from a finger-stick glucose reading. A glucose test tells you what’s happening right now. An A1C tells you what’s been happening for months, which is far more useful for spotting patterns and long-term risk.
What the Numbers Mean
Each percentage point on the A1C scale corresponds to a specific average blood sugar level:
- 5% A1C: roughly 97 mg/dL average blood sugar
- 5.7% A1C: the upper edge of normal
- 6% A1C: roughly 126 mg/dL average (prediabetes range)
- 6.5% A1C: roughly 140 mg/dL average (diabetes threshold)
- 7% A1C: roughly 154 mg/dL average
The conversion follows a straightforward formula: multiply the A1C percentage by 28.7 and subtract 46.7 to get estimated average glucose in mg/dL. But the real takeaway is simpler than the math. Every half-point increase above 5.7% represents meaningfully higher blood sugar exposure over time, and that exposure is what drives complications.
A1C Targets for People With Diabetes
If you already have diabetes, “healthy” shifts. The American Diabetes Association’s 2025 guidelines set a target of below 7% for most nonpregnant adults with diabetes. That corresponds to an average blood sugar around 154 mg/dL. Some people can safely aim lower than 7%, and doing so may offer additional protection, as long as it doesn’t come with frequent episodes of dangerously low blood sugar.
For older adults, the targets are more relaxed. Healthy older adults with diabetes generally aim for below 7.5%. Those with more complex medical situations target below 8%, and people with serious health challenges or limited life expectancy may aim for below 8.5%. The reasoning is practical: aggressive blood sugar lowering carries its own risks, particularly low blood sugar episodes that can cause falls, confusion, or hospitalization. In older adults, those risks can outweigh the benefits of tight control.
When to Get Tested
Current guidelines from both the U.S. Preventive Services Task Force and the American Diabetes Association recommend diabetes screening starting at age 35, with repeat testing every three years if results are normal. If you have risk factors like obesity, a family history of diabetes, or a history of gestational diabetes, your doctor may test earlier or more frequently.
If your result comes back in the prediabetes range (5.7% to 6.4%), more frequent monitoring makes sense. Prediabetes is not a guaranteed path to diabetes. Weight loss of even 5% to 7% of body weight, combined with regular physical activity, can push A1C back into the normal range.
When A1C Can Be Misleading
Because A1C depends on hemoglobin inside red blood cells, anything that changes your red blood cells can throw the number off. This is worth understanding so you don’t get falsely reassured or unnecessarily alarmed.
Conditions that shorten red blood cell lifespan, like hemolytic anemia or recent significant blood loss, give hemoglobin less time to accumulate sugar. The result: a falsely low A1C that looks better than your actual blood sugar control. Conversely, iron deficiency anemia pushes A1C higher through a chemical process that enhances sugar attachment to hemoglobin. This means someone with untreated iron deficiency might get a prediabetes-range reading even with normal blood sugar.
Genetic hemoglobin variants, which are more common in people of African, Mediterranean, and Southeast Asian descent, can also affect accuracy depending on the lab method used. Kidney failure creates chemically modified hemoglobin that interferes with certain tests. And in late pregnancy, iron deficiency (which is common) can raise A1C in women who don’t have diabetes at all. For these situations, doctors may use alternative markers like fructosamine or glycated albumin, or rely more heavily on direct glucose measurements.
A1C During Pregnancy
Major medical organizations recommend screening for diabetes at the first prenatal visit, and A1C is one tool used for that initial check. The same thresholds apply: below 5.7% is normal, 5.7% to 6.4% suggests prediabetes, and 6.5% or above indicates diabetes. However, A1C alone is not reliable for diagnosing gestational diabetes, the type that develops mid-pregnancy. For that, a glucose tolerance test between 24 and 28 weeks of pregnancy remains the standard.
The physiological changes of pregnancy, including increased blood volume and shifts in iron status, make A1C less reliable as pregnancy progresses. A normal early-pregnancy A1C is reassuring, but it doesn’t rule out problems that may develop later.
How to Interpret Your Result
If your A1C is below 5.7%, your average blood sugar over the past few months has been in a healthy range. No action needed beyond retesting in three years if you’re 35 or older. If it’s between 5.0% and 5.4%, you’re solidly in normal territory. Between 5.4% and 5.6% is still technically normal but sits closer to the edge, and some clinicians consider this a signal to pay attention to diet and activity habits before numbers drift higher.
If you land in the prediabetes range, treat it as an early warning with a wide window for change. If your result is 6.5% or above, that’s a diabetes diagnosis, though most doctors will confirm with a repeat test or a second type of blood sugar measurement before starting treatment. In any case, the A1C number is most useful as a trend over time, not as a single verdict. Two readings six months apart tell a much clearer story than one reading alone.