A healthy A1C level is below 5.7%, which translates to an estimated average blood sugar of about 117 mg/dL or lower. This simple blood test measures how much glucose has attached to your red blood cells over the past two to three months, giving you a longer-term picture of blood sugar control than a single finger stick ever could.
What the A1C Test Actually Measures
Glucose in your bloodstream naturally sticks to hemoglobin, the protein inside red blood cells that carries oxygen. This attachment happens in two stages. First, glucose binds loosely in a reversible bond. Then it undergoes a chemical rearrangement into a permanent, stable form. Once that second step happens, the glucose stays locked onto that hemoglobin molecule for the rest of the red blood cell’s life, roughly 8 to 12 weeks.
Your A1C result is the percentage of hemoglobin molecules carrying this permanently attached glucose. The higher your blood sugar has been running over the past two to three months, the more hemoglobin gets tagged. A result of 5.0% means about 5% of your hemoglobin is glycated. A result of 7.0% means more glucose has been circulating, and more hemoglobin shows it.
The Three Diagnostic Ranges
The CDC uses three A1C categories:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
These cutoffs aren’t arbitrary. They correspond to the blood sugar levels at which the risk of diabetes complications, particularly damage to small blood vessels in the eyes and kidneys, begins to climb meaningfully. A result in the prediabetes range means your body is already struggling to manage glucose efficiently, even if you feel fine and your fasting blood sugar looks normal on a given morning.
Converting A1C to Average Blood Sugar
If percentages feel abstract, you can convert your A1C into an estimated average glucose (eAG) using a straightforward formula: multiply your A1C by 28.7, then subtract 46.7. The result is your approximate average blood sugar in mg/dL over the testing period.
Here’s what that looks like in practice:
- A1C of 5.0%: average blood sugar of about 97 mg/dL
- A1C of 5.7%: about 117 mg/dL
- A1C of 6.5%: about 140 mg/dL
- A1C of 7.0%: about 154 mg/dL
- A1C of 8.0%: about 183 mg/dL
This conversion helps connect the dots between the number your doctor reports and the daily blood sugar readings you might see on a glucose monitor.
A1C Targets for People With Diabetes
If you’ve already been diagnosed with diabetes, “healthy” doesn’t necessarily mean getting below 5.7%. Most guidelines recommend a target of 7.0% or lower for adults managing diabetes, which corresponds to an average blood sugar around 154 mg/dL. That target balances good long-term protection against complications with a realistic, sustainable level of blood sugar control.
Pushing aggressively below 7.0% can increase the risk of hypoglycemia, episodes where blood sugar drops low enough to cause shakiness, confusion, or even loss of consciousness. For some people the tradeoff makes sense; for others it doesn’t.
How Targets Shift With Age and Health Status
A1C goals get more flexible as people age or develop other health conditions. For older adults who are functionally independent and otherwise healthy, the standard target of 7.0% or below still applies. But for those who are less independent or managing multiple chronic conditions, guidelines widen the acceptable range to under 8.0%. For older adults who are frail or living with dementia, a target below 8.5% is considered appropriate.
The reasoning is practical. Tight blood sugar control requires careful medication management, frequent monitoring, and consistent eating patterns. For someone whose daily life is already complicated by other health challenges, the risk of dangerous low blood sugar episodes outweighs the benefit of hitting a lower A1C number. Preventing hypoglycemia becomes the priority.
A1C During Pregnancy
Pregnancy is one situation where A1C levels matter more than usual. For women with preexisting type 1 or type 2 diabetes, elevated A1C early in pregnancy increases the risk of miscarriage and birth defects. Those risks become significant when A1C exceeds 8.0%, which corresponds to an average blood sugar above 180 mg/dL. As A1C climbs higher beyond that point, the risk of developmental problems rises progressively. Most providers aim for the tightest blood sugar control possible before and during early pregnancy.
It’s worth noting that A1C readings can be misleading in late pregnancy. Iron deficiency, which is common in the third trimester, can artificially raise A1C results even in women without diabetes. Daily glucose monitoring is typically more reliable than A1C during this period.
When Your A1C Might Be Wrong
Because the test depends on hemoglobin and red blood cell lifespan, anything that disrupts either one can skew results. Several common conditions can make your A1C look higher or lower than your actual blood sugar control warrants.
Conditions that shorten the lifespan of red blood cells, like hemolytic anemia or recovery from significant blood loss, can make A1C appear falsely low. Your red blood cells haven’t been around long enough to accumulate glucose, so the number underestimates your real average. Iron deficiency anemia works in the opposite direction, pushing A1C results falsely high.
Hemoglobin variants, including sickle cell trait and other inherited conditions, can also interfere with the accuracy of certain A1C testing methods. Kidney disease poses its own challenges: chemical changes to hemoglobin in people with kidney failure can throw off results, and for patients on dialysis, A1C tends to underestimate blood sugar levels. In these cases, alternative markers like glycated albumin (a different blood protein that reflects a shorter, two-to-three-week window) may give a more accurate picture.
If you have any of these conditions, a single A1C result shouldn’t be taken at face value. Your provider can use additional tests or adjust their interpretation accordingly.
How Often to Get Tested
If your A1C falls in the normal range and you have no risk factors for diabetes, periodic testing during routine checkups is generally sufficient. If your result lands in the prediabetes range (5.7% to 6.4%), more frequent monitoring helps track whether lifestyle changes are making a difference or whether your blood sugar is trending upward.
For people with diabetes who are meeting their treatment goals with stable blood sugar, testing twice a year is standard. Those who are adjusting medications or not yet at their target typically get tested every three months. Since the test reflects a two-to-three-month average, testing more often than that rarely provides new information.