An A1c number tells you what percentage of your hemoglobin, a protein in red blood cells, has glucose attached to it. A result below 5.7% is normal, 5.7% to 6.4% indicates prediabetes, and 6.5% or higher means diabetes. Unlike a finger-stick blood sugar reading that captures a single moment, the A1c reflects your average blood sugar over roughly three months.
How the Test Works
Glucose in your bloodstream naturally sticks to hemoglobin inside red blood cells. The higher your blood sugar runs over time, the more hemoglobin gets coated with glucose. Since red blood cells live about three months before your body replaces them, the A1c test essentially reads a rolling average of your blood sugar across that entire lifespan. A result of 7%, for example, doesn’t mean your blood sugar was at one fixed level for 90 days. It means the overall average landed in a range that corresponds to roughly 154 mg/dL.
What Each Range Means
The three diagnostic categories are straightforward:
- Below 5.7%: Normal blood sugar regulation. Your body is producing and using insulin effectively.
- 5.7% to 6.4%: Prediabetes. Blood sugar is elevated but not yet in the diabetes range. This is the window where lifestyle changes, like losing a modest amount of weight and increasing physical activity, can often prevent progression to type 2 diabetes.
- 6.5% or higher: Diabetes. A doctor will typically confirm with a second test before making an official diagnosis, unless you also have clear symptoms like excessive thirst, frequent urination, or unexplained weight loss.
For people already managing diabetes, the general goal is to keep A1c below 7%. But this target isn’t universal. Older adults with multiple health conditions may aim for a slightly higher number, since pushing blood sugar too low carries its own risks, including dizziness, confusion, and falls. During pregnancy, the target is lower than usual because even moderately elevated blood sugar can affect the developing baby.
Converting A1c to Average Blood Sugar
One reason A1c numbers can feel abstract is that they’re expressed as percentages rather than the mg/dL readings you’d see on a glucose meter. The conversion formula is: multiply your A1c by 28.7, then subtract 46.7. That gives you your estimated average glucose (eAG) in mg/dL.
Here’s what common A1c values translate to in practical terms:
- 6% A1c: ~126 mg/dL average
- 6.5%: ~140 mg/dL
- 7%: ~154 mg/dL
- 8%: ~183 mg/dL
- 9%: ~212 mg/dL
- 10%: ~240 mg/dL
Each full percentage point of A1c corresponds to roughly a 29 mg/dL change in average blood sugar. So dropping from 8% to 7% means your daily average fell by about 29 mg/dL, which represents a meaningful reduction in the strain high blood sugar places on blood vessels, nerves, and organs.
When A1c Can Be Misleading
The test is reliable for most people, but certain conditions can skew results in either direction. Anything that shortens the life of your red blood cells, like significant blood loss or certain types of anemia where red blood cells break down faster than normal, will make A1c read artificially low. Your hemoglobin simply hasn’t been circulating long enough to accumulate glucose proportional to your actual blood sugar levels.
Iron deficiency anemia pushes results the opposite way, making A1c read higher than expected. This is also why A1c can be falsely elevated in late pregnancy, when iron deficiency is common even in women without diabetes.
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 disease on dialysis is another situation where A1c becomes less reliable as a marker of blood sugar control. In these cases, doctors may rely on alternative tests or combine A1c with daily glucose monitoring for a clearer picture.
How Often to Get Tested
If you have diabetes, expect an A1c test at least twice a year. People whose treatment plan has recently changed, or whose blood sugar isn’t yet at target, may need testing every three months. For someone without diabetes, A1c is typically part of routine screening 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 reflects a three-month window, checking more frequently than every 12 weeks won’t capture meaningful change. If you’ve started a new medication or made significant diet changes, give it a full three months before expecting your A1c to reflect the results.