A normal A1C for a healthy adult is below 5.7%. The national average for adults without diabetes falls between roughly 5.0% and 5.5%, depending on age. An A1C of 5.7% to 6.4% signals prediabetes, and 6.5% or higher means diabetes.
What A1C Actually Measures
A1C reflects your average blood sugar over the past two to three months. It works by measuring the percentage of hemoglobin (the oxygen-carrying protein in red blood cells) that has glucose attached to it. The higher your blood sugar has been running, the more glucose sticks to hemoglobin. Because red blood cells live about 90 to 120 days, the test captures a rolling average rather than a single-moment snapshot.
Normal, Prediabetes, and Diabetes Ranges
The American Diabetes Association defines three tiers:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
These cutoffs apply to most adults. If you already have diabetes, the general treatment target is an A1C below 7%, though your doctor may set a different goal based on your age, health history, and risk of low blood sugar episodes.
How A1C Translates to Daily Blood Sugar
A1C percentages can feel abstract. The conversion to estimated average glucose (eAG) makes them more concrete. Each percentage point corresponds to roughly 29 mg/dL of average blood sugar:
- A1C 5%: average glucose around 97 mg/dL
- A1C 6%: around 126 mg/dL
- A1C 7%: around 154 mg/dL
- A1C 8%: around 183 mg/dL
- A1C 9%: around 212 mg/dL
- A1C 10%: around 240 mg/dL
These are averages with some individual variation. Two people with the same A1C of 7% could have true average glucose readings anywhere from roughly 123 to 185 mg/dL.
How Average A1C Changes With Age
A1C naturally drifts upward as you get older, even if you never develop diabetes. Data from two large U.S. population studies (the Framingham Offspring Study and NHANES) show that nondiabetic adults under 40 average about 5.0% to 5.2%, while those 70 and older average about 5.4% to 5.5%. That works out to roughly a 0.01 percentage point increase per year of life.
This age-related creep matters because an A1C of 5.6% means something different for a 25-year-old than for a 75-year-old. In the Framingham data, the upper limit of normal (97.5th percentile) for people under 40 was 5.6% to 6.0%, while for those over 70 it was 6.2% to 6.6%. The standard diagnostic cutoffs don’t adjust for age, so older adults may be flagged as prediabetic even when their blood sugar levels are typical for their age group.
National survey data also show differences across age brackets for the broader U.S. population (including people with undiagnosed blood sugar issues). Adults aged 18 to 64 cluster around 5.0% to 5.7%, while those 65 and older range from about 5.3% to 6.0%, depending on individual variation in how quickly glucose attaches to hemoglobin.
Why Your A1C Might Not Be Accurate
Several conditions can push your A1C reading higher or lower than your actual blood sugar warrants. Knowing these is important because a misleading result could lead to unnecessary treatment or missed diabetes.
Conditions That Falsely Lower A1C
Anything that shortens the lifespan of your red blood cells gives glucose less time to attach to hemoglobin, pulling the number down. This includes recovery from significant blood loss, hemolytic anemia (where red blood cells break down faster than normal), sickle cell disease, and kidney failure requiring dialysis. If your red blood cells are turning over quickly, your A1C may look reassuringly low while your actual blood sugar is elevated.
Conditions That Falsely Raise A1C
Iron deficiency anemia is the most common culprit. When you’re low on iron, red blood cells live longer and accumulate more glucose on their hemoglobin, inflating the result. This is particularly relevant during late pregnancy, when iron deficiency is common and can raise A1C in women who don’t have diabetes at all.
Hemoglobin Variants
Certain inherited forms of hemoglobin, more common in people with ancestry from Africa, South and Southeast Asia, or the Mediterranean, can interfere with how the test is performed. Depending on the lab method used, these variants can push results in either direction. Having a hemoglobin variant doesn’t change your diabetes risk, but it can make the A1C test less reliable. If your results don’t match what your fingerstick or continuous glucose readings suggest, a variant could be the reason.
How Often A1C Is Tested
If you have diabetes and your blood sugar is stable and on target, testing twice a year is standard. If your treatment plan recently changed or you’re not meeting your goals, testing every three months gives a more current picture. For people without diabetes, A1C is typically checked as part of routine screening, especially after age 35 or if you have risk factors like excess weight, family history, or a history of gestational diabetes.
What a Prediabetes Result Means in Practice
An A1C between 5.7% and 6.4% isn’t a diabetes diagnosis, but it’s not a number to ignore. It means your blood sugar is running higher than normal, and without changes, about 15% to 30% of people with prediabetes develop type 2 diabetes within five years. The encouraging side: moderate weight loss (5% to 7% of body weight) and regular physical activity can drop A1C back into the normal range and significantly cut that risk. A 200-pound person losing 10 to 14 pounds, combined with about 150 minutes of walking or similar exercise per week, is the combination with the strongest evidence behind it.