The A1C test measures your average blood sugar over the past two to three months, and results fall into three ranges: normal is below 5.7%, prediabetes is 5.7% to 6.4%, and diabetes is 6.5% or above. These cutoffs, used by the CDC and the American Diabetes Association, determine whether your blood sugar control is healthy, trending in a concerning direction, or has crossed into diabetic territory.
The Three A1C Ranges
A1C is reported as a percentage. The higher your blood sugar has been running, the higher the percentage.
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
A result of 5.7% to 6.4% means your blood sugar is higher than it should be but hasn’t reached the diabetes threshold. About 80% of people with prediabetes don’t know they have it, so this range often comes as a surprise. The good news is that prediabetes is reversible with changes to diet, activity, and weight.
A result at or above 6.5% on two separate tests confirms a diabetes diagnosis. Once someone has diabetes, the typical treatment target is an A1C below 7.0%, though this varies by individual.
What A1C Actually Measures
Glucose in your bloodstream sticks to hemoglobin, the protein inside red blood cells that carries oxygen. Once glucose binds to hemoglobin, it stays attached for the life of that red blood cell, which is roughly 120 days. The A1C test measures what percentage of your hemoglobin has glucose stuck to it.
Not all of those 120 days count equally, though. About half of the glycation reflected in your A1C happened in just the last 30 days. Another 40% comes from the previous one to three months, and only about 10% reflects anything beyond 90 days. This means your most recent weeks of blood sugar control have the biggest influence on your result.
How A1C Translates to Daily Blood Sugar
If you check blood sugar with a finger stick or continuous monitor, you see numbers in mg/dL. Your A1C maps 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 5.7% (prediabetes threshold): approximately 117 mg/dL average
- A1C 6.0%: 126 mg/dL average
- A1C 6.5% (diabetes threshold): 140 mg/dL average
- A1C 7.0% (common treatment target): 154 mg/dL average
- A1C 8.0%: 183 mg/dL average
- A1C 9.0%: 212 mg/dL average
- A1C 10.0%: 240 mg/dL average
These are averages, so they don’t tell you about spikes and dips throughout the day. Two people can have the same A1C but very different daily patterns. One might hold steady around 154 mg/dL, while another swings between 80 and 230, averaging the same number.
Target Ranges for People With Diabetes
Once you have a diabetes diagnosis, the goal shifts from the diagnostic cutoffs to a treatment target. For most adults with diabetes, that target is below 7.0%. But this isn’t one-size-fits-all.
Older adults or people with a history of severe low blood sugar episodes may aim for a slightly higher target, sometimes below 7.5% or 8.0%, because aggressively lowering blood sugar can cause dangerous drops. On the other end, younger adults who are otherwise healthy and newly diagnosed sometimes aim for 6.5% or lower.
Pregnancy calls for tighter control. Women with pre-existing diabetes who are planning to conceive are generally advised to reach an A1C of 6.5% or below before pregnancy. During pregnancy itself, especially by the third trimester, an A1C at or below 6.1% is ideal because the risk of complications, including stillbirth, rises above that level. These tighter targets are only appropriate when they can be achieved without frequent episodes of dangerously low blood sugar.
When A1C Results Can Be Misleading
Because the test depends on red blood cells, anything that changes how long your red blood cells live or how hemoglobin behaves can skew results. This is worth knowing if your number doesn’t match what you’d expect from your daily blood sugar readings.
Conditions that shorten red blood cell lifespan, like hemolytic anemia or recent significant blood loss, will make your A1C falsely low. Your red blood cells haven’t been around long enough to accumulate the expected amount of glucose, so the test underestimates your true average.
Iron deficiency anemia does the opposite. It’s associated with falsely high A1C readings, and treating the iron deficiency with supplements lowers the A1C even without any change in blood sugar. This is particularly relevant during late pregnancy, when iron deficiency is common and can inflate A1C in women who don’t actually have diabetes.
Certain hemoglobin variants, including sickle cell trait and hemoglobin C trait, can also interfere with results depending on the lab method used. People with chronic kidney disease face multiple sources of interference: a chemically altered form of hemoglobin, anemia from kidney dysfunction, and the effects of dialysis all make A1C less reliable. For these patients, alternative tests that measure glucose attachment to other proteins may give a more accurate picture.
How Often to Get Tested
If your A1C is normal, testing every three years is a reasonable screening interval for most adults, though your doctor may test more often if you have risk factors like obesity, a family history of diabetes, or a history of gestational diabetes. If you’re in the prediabetes range, annual testing helps track whether your blood sugar is improving or progressing toward diabetes.
For people already managing diabetes, testing typically happens every three to six months. If your treatment has recently changed or your blood sugar isn’t well controlled, testing every three months makes sense because it takes roughly that long for a new medication or lifestyle change to fully show up in the A1C result. Once your levels are stable and at target, twice a year is usually sufficient.