A good A1c is below 5.7%, which falls in the normal range and means your average blood sugar over the past two to three months has been healthy. If you already have diabetes, the target shifts: most adults aim for below 7%, though your ideal number depends on your age, health, and risk of low blood sugar episodes.
What A1c Measures
A1c reflects how much glucose has attached to the hemoglobin inside your red blood cells. Because red blood cells live about 120 days, the test captures a rolling average of your blood sugar rather than a single snapshot. The weighting isn’t even across those months, though. Roughly half the result comes from the most recent 30 days, about 40% from days 31 through 90, and only 10% from beyond that. A lifestyle change you made last week won’t show up much yet, but one you made six weeks ago will.
Each percentage point translates to a concrete average blood sugar. An A1c of 6% corresponds to an estimated average glucose of about 126 mg/dL. At 7%, that rises to 154 mg/dL. By 8%, it’s roughly 183 mg/dL. These conversions help bridge the gap between the percentage your lab reports and the numbers you see on a home glucose meter.
The Three Diagnostic Ranges
Clinicians use A1c to sort results into three categories:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
A result in the prediabetes range doesn’t mean diabetes is inevitable. It means your blood sugar has been running higher than ideal and the trend is worth reversing. Moderate weight loss, regular physical activity, and dietary changes can bring a prediabetic A1c back below 5.7% for many people.
A1c Targets if You Have Diabetes
For most nonpregnant adults with diabetes, the American Diabetes Association recommends an A1c below 7%. That threshold balances meaningful protection against complications with a realistic risk of low blood sugar. Going lower is fine, and even beneficial, as long as you can get there safely without frequent or severe drops in blood sugar.
The risk of complications climbs as A1c rises. Research published in Diabetes Care found that microvascular complications, including eye disease, kidney damage, and amputations, increased significantly once A1c reached 7.2% or above. Below that level, across a range from about 5% to 7.1%, there was no statistically significant difference in risk. That’s one reason 7% serves as the standard cutoff: it’s the approximate threshold where complication rates start to separate.
When the Target Is Higher
A lower A1c isn’t always better. For some people, aggressively pushing blood sugar down creates more danger from hypoglycemia than the long-term benefit is worth. Guidelines from both the ADA and Diabetes Canada outline situations where a higher target makes sense:
- Older adults who are functionally independent still aim for 7% or below, but those who depend on others for daily activities may target 7.1% to 8.0%.
- People with frailty or dementia generally have a target of 7.1% to 8.5%, prioritizing the avoidance of dangerous blood sugar lows over tight control.
- Anyone with frequent or severe low blood sugar episodes should raise their target, regardless of age. Repeated hypoglycemia is an absolute reason to adjust treatment goals upward.
- People near the end of life typically stop A1c testing altogether. The focus shifts to comfort, avoiding symptoms of very high or very low blood sugar without chasing a number.
These aren’t failures of diabetes management. They reflect the reality that the “best” A1c is the one that keeps you safe and functioning well given your full health picture.
A1c Targets During Pregnancy
Pregnancy tightens the goal considerably. For women with preexisting diabetes planning a pregnancy, the ADA recommends getting A1c below 6.5% before conception to reduce the risk of birth defects, preeclampsia, and preterm delivery. Once pregnant, the ideal target drops further to below 6% if that’s achievable without significant low blood sugar. If hypoglycemia becomes a problem, the goal can be relaxed to below 7%.
Standard A1c-to-glucose conversions aren’t reliable during pregnancy because blood volume and red blood cell turnover change. Your care team will rely more heavily on direct glucose monitoring during those months.
Conditions That Affect Accuracy
Because the test depends on hemoglobin inside red blood cells, anything that changes those cells can skew the result. Iron-deficiency anemia, sickle cell trait, significant blood loss, blood transfusions, and conditions that cause red blood cells to break down faster than normal (hemolytic anemia) can all produce A1c readings that don’t match your actual blood sugar levels. If you have any of these conditions, your doctor may use alternative tests, like fructosamine, to get a more accurate picture.
How Often to Test
Testing frequency depends on where you stand. If you have prediabetes, once a year is typically enough to track whether things are stable or trending in the wrong direction. If you have diabetes and your blood sugar is well controlled without insulin, twice a year is standard. People who use insulin, have recently changed medications, or are struggling to stay in their target range may need testing every three months or more. Since the test heavily reflects the most recent 30 days, retesting sooner than about 8 weeks after a treatment change won’t give you a full picture of the adjustment’s effect.