How it works
The Hemoglobin A1c (HbA1c) test measures the percentage of your red blood cells with glucose-coated hemoglobin over the preceding 2 to 3 months (the natural lifespan of a red blood cell). Because daily fingerstick readings fluctuate constantly with meals, stress, and exercise, HbA1c and its translated Estimated Average Glucose (eAG) provide the clinical benchmark for diagnosing diabetes, monitoring prediabetes, and evaluating glycemic treatment plans.
eAG (mg/dL) = 28.7 × HbA1c − 46.7 eAG (mmol/L) = (28.7 × HbA1c − 46.7) ÷ 18.0182 · HbA1c (%) = (eAG_mgdl + 46.7) ÷ 28.7Worked example. A laboratory HbA1c blood test result is 7.0%. Applying the clinical Nathan et al. formula: eAG = 28.7 × 7.0 − 46.7 = 200.9 − 46.7 = 154 mg/dL (exactly 154.2 mg/dL). In international metric units, dividing 154.2 by 18.0182 yields 8.6 mmol/L. This result falls into the Diabetes range (diagnostic threshold ≥ 6.5%), while successfully achieving the universal American Diabetes Association target of < 7.0% for most non-pregnant adult diabetes patients.
Clinical HbA1c diagnostic thresholds (ADA 2026)
The American Diabetes Association (ADA) and International Expert Committee establish the following official diagnostic criteria for non-pregnant adults:
- Normal: HbA1c below 5.7% (eAG below 117 mg/dL or 6.5 mmol/L). Indicates healthy carbohydrate metabolism and low diabetes risk.
- Prediabetes: HbA1c between 5.7% and 6.4% (eAG 117 to 137 mg/dL or 6.5 to 7.6 mmol/L). Signals elevated insulin resistance and substantial risk of progression to type 2 diabetes without dietary and lifestyle intervention.
- Diabetes: HbA1c of 6.5% or higher on two separate tests (eAG 140 mg/dL or 7.8 mmol/L and above). Confirms a diagnosis of diabetes requiring medical management.
Common HbA1c and daily blood sugar equivalents
| HbA1c (%) | Average Glucose (mg/dL) | Average Glucose (mmol/L) | Clinical Classification |
|---|---|---|---|
| 5.0% | 97 mg/dL | 5.4 mmol/L | Normal |
| 5.5% | 111 mg/dL | 6.2 mmol/L | Normal |
| 5.7% | 117 mg/dL | 6.5 mmol/L | Prediabetes threshold |
| 6.0% | 126 mg/dL | 7.0 mmol/L | Prediabetes |
| 6.5% | 140 mg/dL | 7.8 mmol/L | Diabetes diagnostic threshold |
| 7.0% | 154 mg/dL | 8.6 mmol/L | Standard ADA adult target |
| 7.5% | 169 mg/dL | 9.4 mmol/L | Sub-optimal control |
| 8.0% | 183 mg/dL | 10.2 mmol/L | Elevated complication risk |
| 9.0% | 212 mg/dL | 11.8 mmol/L | High risk — clinical review needed |
How does eAG differ from daily meter readings?
Your home glucose meter or continuous glucose monitor (CGM) measures your immediate blood sugar at a single point in time. In contrast, eAG (Estimated Average Glucose) represents a weighted 24-hour average across approximately 90 days, incorporating fasting periods, post-meal spikes, and overnight readings. It is normal for fasting glucose to be lower than eAG, and for post-meal readings to be higher.
Managing metabolic wellness also involves tracking body composition and lifestyle factors. Check your body mass index with our BMI calculator, calculate your daily caloric energy expenditure using the calorie calculator, and find your healthy weight parameters with the ideal weight calculator.