A healthy A1c level is below 5.7%. This number represents your average blood sugar over the past two to three months, giving you a much broader picture than a single finger-stick reading. If your result falls between 5.7% and 6.4%, you’re in the prediabetes range, and 6.5% or higher means diabetes.
What A1c Actually Measures
Glucose in your bloodstream naturally sticks to hemoglobin, the protein inside red blood cells that carries oxygen. This attachment happens continuously throughout a red blood cell’s lifespan of roughly 8 to 12 weeks. The more glucose circulating in your blood during that window, the more hemoglobin gets coated. An A1c test measures the percentage of your hemoglobin with glucose attached, which is why it reflects an average rather than a single moment in time.
To put the percentages in more familiar terms, an A1c of 6% corresponds to an estimated average blood sugar of about 126 mg/dL. At 6.5% (the diabetes threshold), that average rises to around 140 mg/dL. At 7%, it’s roughly 154 mg/dL. The conversion formula is straightforward: multiply your A1c by 28.7, then subtract 46.7 to get your estimated average glucose in mg/dL.
The Three A1c Categories
- Normal: Below 5.7%. Your blood sugar regulation is working well.
- Prediabetes: 5.7% to 6.4%. Blood sugar is elevated but not yet in the diabetes range. This is the window where lifestyle changes, particularly diet and exercise, have the strongest evidence for preventing progression.
- Diabetes: 6.5% or higher. The American Diabetes Association uses this as the diagnostic cutoff, though your doctor will typically confirm with a repeat test or a second type of blood sugar measurement.
A1c Targets if You Have Diabetes
For most non-pregnant adults with diabetes, the recommended goal is an A1c below 7%. This target balances meaningful reduction in long-term complications (damage to eyes, kidneys, nerves, and blood vessels) with an acceptable risk of blood sugar dropping too low. Going lower than 7% can be beneficial if you can get there safely, without frequent episodes of low blood sugar or side effects from medication.
Not everyone should aim for the same number, though. Older adults, people with multiple chronic conditions, or those who experience dangerous drops in blood sugar may do better with a less aggressive target. The reasoning is practical: tight blood sugar control requires more medication and carries a higher risk of hypoglycemia, which can cause falls, confusion, and heart problems. For someone with a limited life expectancy or significant frailty, the long-term benefits of strict control may not outweigh the immediate risks. In these situations, simplifying treatment and preventing symptoms becomes the priority.
How Often to Get Tested
If your A1c is stable and you’re meeting your target, testing twice a year is generally sufficient. When your blood sugar isn’t well controlled or your treatment plan has recently changed, quarterly testing (every three months) is more useful. Research from a large observational study published in Diabetes Care found that testing every three months was associated with a 3.8% reduction in A1c over time, compared to a 1.5% increase with annual testing. Testing more frequently than quarterly didn’t provide additional benefit.
When A1c Results Can Be Misleading
Because the test depends on hemoglobin and red blood cells, anything that changes those components can skew results. Iron deficiency anemia, for example, tends to push A1c readings falsely higher, meaning your actual average blood sugar may be lower than the test suggests. On the other hand, conditions that shorten the lifespan of red blood cells, like hemolytic anemia or recent significant blood loss, can make A1c read falsely low because the hemoglobin hasn’t been circulating long enough to accumulate glucose.
Kidney disease also complicates things. In people on dialysis, chemical changes to hemoglobin can distort results, and some specialists rely on alternative markers to track blood sugar control in these patients.
Certain inherited hemoglobin variants, including types S, C, D, and E, can interfere with some testing methods. These variants are more common in people with ancestry from Africa, South and Southeast Asia, and the Mediterranean. If you carry one of these variants, some A1c testing methods may give falsely high or falsely low readings. A falsely high result could lead to unnecessary medication increases, while a falsely low result might mask poorly controlled blood sugar. If your A1c results don’t seem to match your daily blood sugar readings, this is worth discussing with your doctor, as different testing methods handle hemoglobin variants differently.
What Moves Your A1c
Since A1c reflects a two- to three-month average, you won’t see changes overnight. A single week of high blood sugar from illness or holiday eating barely registers, but sustained patterns do. The most recent four to six weeks contribute more heavily to the result than the earlier weeks, because newer red blood cells make up a larger share of the sample.
For people in the prediabetes range, modest changes often produce meaningful results. Losing 5% to 7% of body weight and getting 150 minutes of moderate activity per week have been shown in large trials to cut the risk of progressing to diabetes nearly in half. These same habits tend to bring A1c down by a few tenths of a percentage point, which matters more than it sounds when you’re sitting just above the 5.7% line.
For people managing diabetes, A1c responds to the full picture: what you eat, how active you are, how well your medications are working, your sleep quality, and even stress levels. A drop of just one percentage point in A1c is associated with significant reductions in the risk of complications affecting the eyes, kidneys, and nerves. Small, sustained improvements add up over years in ways that single blood sugar readings never capture.