A normal A1c is below 5.7%. This means your average blood sugar over the past two to three months has been in a healthy range. An A1c between 5.7% and 6.4% falls into the prediabetes zone, and 6.5% or higher indicates diabetes.
What the A1c Test Actually Measures
The A1c test measures the percentage of your hemoglobin (a protein in red blood cells) that has glucose stuck to it. When sugar circulates in your blood, some of it naturally binds to hemoglobin through a chemical reaction. The more sugar in your blood over time, the more hemoglobin gets coated.
Because red blood cells live for about 120 days, the A1c captures a weighted average of your blood sugar over roughly the past three months. It’s not an even snapshot of that entire window, though. About half of the result reflects your blood sugar from just the last 30 days. Another 40% comes from the month or two before that, and only about 10% reflects anything beyond 90 days. So recent weeks matter more than you might think.
This makes the A1c different from a finger-stick glucose reading, which only tells you what your blood sugar is at that exact moment. A single fasting glucose can swing based on what you ate last night, how well you slept, or whether you’re stressed. The A1c smooths all of that out into one number.
A1c Ranges and What They Mean
Both the CDC and the American Diabetes Association use the same cutoffs:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
If your result comes back at 5.7% or above, it doesn’t necessarily mean you’ll develop diabetes. Prediabetes is a signal that your blood sugar regulation is under strain, and lifestyle changes at this stage, particularly losing a modest amount of weight and increasing physical activity, can push the number back below 5.7%.
A result of 6.5% or higher is typically confirmed with a second test before a diabetes diagnosis is made, because a single test can sometimes be thrown off by other factors.
How A1c Translates to Daily Blood Sugar
If you’ve ever checked your blood sugar with a meter, it helps to know what your A1c corresponds to in those everyday numbers. The conversion formula is straightforward: multiply your A1c by 28.7, then subtract 46.7. That gives you your estimated average glucose in mg/dL.
Here’s what that looks like in practice:
- A1c of 5.7%: roughly 117 mg/dL average
- A1c of 6.0%: roughly 126 mg/dL average
- A1c of 6.5%: roughly 140 mg/dL average
- A1c of 7.0%: roughly 154 mg/dL average
- A1c of 8.0%: roughly 183 mg/dL average
- A1c of 9.0%: roughly 212 mg/dL average
Keep in mind that “average” means your blood sugar was sometimes higher and sometimes lower than that number. Two people with the same A1c can have very different daily patterns: one might stay relatively steady, while the other swings between highs and lows that average out to the same result.
A1c Targets During Pregnancy
For people who are pregnant or planning a pregnancy, the targets are tighter than the general population. Before conception, the goal is an A1c below 6.5% to reduce the risk of birth complications including congenital anomalies, preeclampsia, and preterm delivery. During the second and third trimesters, the ideal target drops further to below 6.0%, as long as that level can be maintained safely without episodes of dangerously low blood sugar. When that’s not realistic, a target below 7.0% is considered acceptable.
How Age Affects Target Ranges
The “below 5.7%” threshold for normal applies across all ages. But for people already managing diabetes, the treatment targets shift with age. Younger adults are generally held to stricter goals, sometimes as low as 6.0% to 6.5%, because tighter control over decades helps prevent complications affecting the eyes, kidneys, and cardiovascular system.
For older adults, particularly those over 75 or living with multiple health conditions, targets are often relaxed to 7.5% or even 8.0%. The reasoning is practical: aggressive blood sugar lowering in older people carries a greater risk of dangerous lows, which can cause falls, confusion, and hospitalization. Preventing those immediate harms takes priority over long-term complication reduction.
When Your A1c Might Be Misleading
The A1c test assumes your red blood cells have a typical lifespan. When that assumption breaks down, the number on your lab report may not reflect your true blood sugar average.
Iron deficiency anemia is one of the most common conditions that skews results. It causes red blood cells to live longer than usual, which gives glucose more time to accumulate on hemoglobin. The result: a falsely high A1c. Research shows that treating iron deficiency with supplementation lowers A1c even without any change in actual blood sugar levels.
On the other side, any condition that shortens red blood cell life will produce a falsely low A1c. This includes hemolytic anemias (where the body destroys red blood cells faster than normal), recent significant blood loss, and chronic kidney disease, especially in people on dialysis. In those situations, the red blood cells simply don’t live long enough to accumulate a representative amount of glucose.
Certain inherited hemoglobin variants, including sickle cell trait and hemoglobin C trait, can also affect A1c accuracy. The impact depends on the specific variant and the testing method the lab uses. If you carry one of these traits, your provider may recommend an alternative test like fructosamine, which measures glucose attached to blood proteins that turn over every two to three weeks rather than three months.
How Often to Get Tested
If your A1c is normal and you have no risk factors for diabetes, testing every three years starting at age 35 is a reasonable schedule (or earlier if you have a family history, are overweight, or have other risk factors). If your result falls in the prediabetes range, repeat testing every one to two years helps track whether lifestyle changes are working or whether the number is climbing. For people with diabetes, the test is typically done two to four times per year depending on how stable blood sugar levels have been.
Because the test reflects a rolling average heavily weighted toward the last month, timing matters if you’re tracking progress. Getting tested too soon after making changes, say two or three weeks into a new exercise routine, won’t show much difference yet. Waiting at least three months gives the result time to catch up to your new habits.