What is A1C?
A1C (also written HbA1c) is a blood test that measures the percentage of your hemoglobin that has glucose attached to it. Because red blood cells live about 90 days, the A1C test reflects your average blood sugar over the previous two to three months — making it the gold-standard test for diagnosing and monitoring diabetes.
What does A1C measure?
When glucose circulates in your blood, some of it binds to hemoglobin in your red blood cells. The more glucose in your blood, the more glycated hemoglobin you accumulate. The A1C percentage tells your doctor how much glucose your red blood cells have absorbed over their roughly 3-month lifespan.
How does A1C convert to average glucose?
The ADAG study produced the formula most clinicians use to translate A1C into estimated average glucose (eAG): eAG (mg/dL) = 28.7 × A1C − 46.7. Divide by 18.0182 for mmol/L. Use our free A1C calculator to convert instantly, or browse the full A1C to eAG conversion chart.
Normal A1C levels and diabetes diagnosis
Below 5.7% is normal. An A1C between 5.7% and 6.4% indicates prediabetes — a warning sign that lifestyle changes can help reverse. An A1C of 6.5% or higher, confirmed on a second test, indicates diabetes.
How to lower your A1C
Lowering A1C takes sustained effort: reduce refined carbohydrates and added sugar, move more after meals, manage stress, prioritize sleep, stay hydrated, and follow your clinician's treatment plan. A1C improves slowly — about 1% drop takes roughly three months of consistent change. Always check with your doctor before changing anything.