HbA1c (glycated hemoglobin) is the percentage of hemoglobin molecules in red blood cells that have glucose irreversibly attached. Because red cells live about 120 days, HbA1c reflects average blood glucose over the preceding 2–3 months and does not require fasting.

🩸 HbA1c Calculator Glycated Hemoglobin ↔ eAG

Q: What are normal and diabetic HbA1c levels?

Per ADA: < 5.7% normal; 5.7–6.4% prediabetes; ≥ 6.5% diabetes (confirmed on two separate tests). Most adults with diabetes should target < 7.0%, though targets are individualized by age, comorbidities, hypoglycemia risk, and life expectancy.

Q: What is eAG (estimated average glucose)?

eAG translates HbA1c into the same units (mg/dL or mmol/L) that patients see on glucose meters and CGMs, making comparisons intuitive. The ADAG formula is eAG (mg/dL) = 28.7 × HbA1c − 46.7.

Q: When is HbA1c unreliable?

HbA1c can be misleading in conditions that alter red cell lifespan: hemolytic anemia, recent transfusion, major blood loss, iron-deficiency anemia, chronic kidney disease with erythropoietin therapy, pregnancy, and hemoglobinopathies (HbS, HbC, HbE). In these cases, use fructosamine, CGM-derived glucose management indicator (GMI), or direct fasting/2-hour glucose.

Convert HbA1c to estimated average glucose (eAG) in both mg/dL and mmol/L. Based on the ADAG (A1c-Derived Average Glucose) equation.

HbA1c (%) Glycated hemoglobin, DCCT units

📊 Results

📋 HbA1c Classification (ADA)

Category	HbA1c (%)	eAG (mg/dL)	Interpretation
Normal	< 5.7	< 117	Normal glucose regulation
Prediabetes	5.7 – 6.4	117 – 137	Increased risk of diabetes; intensive lifestyle intervention
Diabetes	≥ 6.5	≥ 140	Diabetes mellitus (confirm with a second test)

📊 HbA1c ↔ eAG Conversion Table

HbA1c (%)	eAG (mg/dL)	eAG (mmol/L)
5.0	97	5.4
5.5	111	6.2
6.0	126	7.0
6.5	140	7.8
7.0	154	8.6
7.5	169	9.4
8.0	183	10.2
8.5	197	10.9
9.0	212	11.8
9.5	226	12.6
10.0	240	13.3

📐 Formulas

ADAG equation (HbA1c → eAG)
eAG (mg/dL) = 28.7 × HbA1c − 46.7

Inverse (eAG → HbA1c)
HbA1c (%) = (eAG + 46.7) / 28.7

Unit conversion
eAG (mmol/L) = eAG (mg/dL) / 18

❓ Frequently Asked Questions

What is HbA1c? ▼

HbA1c (glycated hemoglobin) is the percentage of hemoglobin with glucose irreversibly attached. Because red cells circulate ~120 days, HbA1c reflects average glucose over 2–3 months. It is the primary long-term marker of glycemic control and does not require fasting.

What are normal and diabetic HbA1c levels? ▼

ADA thresholds: < 5.7% normal, 5.7–6.4% prediabetes, ≥ 6.5% diabetes (confirm on two separate tests unless overtly symptomatic hyperglycemia). General target for most adults with diabetes is < 7.0%, though individualized targets (6.0–8.0%) apply based on age, comorbidity, and hypoglycemia risk.

What is eAG? ▼

Estimated Average Glucose translates HbA1c into the units patients see on glucose meters and CGMs. It comes from the 2008 ADAG study (Nathan et al., Diabetes Care) using CGM data from 507 subjects. eAG makes HbA1c actionable at the patient level.

When is HbA1c unreliable? ▼

Any condition that changes red cell turnover: hemolytic anemia, recent transfusion, major blood loss, iron-deficiency anemia (can falsely elevate HbA1c), CKD with ESA therapy, pregnancy, and hemoglobinopathies (HbS, HbC, HbE). In these settings use fructosamine, CGM-derived GMI, or fasting/2-hour glucose for diagnosis.

🔗 Related Calculators

About HbA1c

Glycated hemoglobin (HbA1c) reflects average blood glucose over the preceding 2–3 months — the lifespan of circulating red blood cells. Unlike fasting glucose or OGTT, it does not require preparation and is less influenced by day-to-day fluctuations.

The American Diabetes Association (ADA) and WHO endorse HbA1c ≥ 6.5% as a diagnostic criterion for diabetes, confirmed on a second test.

✅ Action Guide by HbA1c Level

Normal HbA1c < 5.7%

Maintain healthy diet and physical activity. Re-screen every 3 years in low-risk adults, or annually if BMI ≥ 25 and one additional risk factor.

Prediabetes HbA1c 5.7–6.4%

Intensive lifestyle intervention (DPP protocol): 5–7% weight loss, ≥ 150 min/week moderate activity, dietary modification. Consider metformin if BMI ≥ 35, age < 60, or prior gestational diabetes. Recheck annually.

Early Diabetes HbA1c 6.5–7.0%

Initiate metformin unless contraindicated. Add SGLT2 inhibitor or GLP-1 receptor agonist if ASCVD, heart failure, or CKD is present. Begin annual screening for retinopathy, neuropathy, and nephropathy.

Active Management HbA1c 7.0–9.0%

Intensify therapy — dual or triple oral agents, or basal insulin. Reassess HbA1c every 3 months until at target, then every 6 months. Monitor for medication side effects and hypoglycemia.

Urgent Management HbA1c > 9.0%

Consider insulin initiation, especially with symptomatic hyperglycemia, weight loss, or ketosis. Exclude acute illness, steroid use, or medication nonadherence. Rapid complication screening is warranted.

🔗 Next Steps

→ HOMA-IR — assess insulin resistance in prediabetes and early type 2 diabetes
→ eGFR — screen for diabetic kidney disease (DKD)
→ Blood pressure — aggressive BP control reduces microvascular and macrovascular events
→ LDL cholesterol — statin recommended in most adults with diabetes aged 40–75

⚠️ Disclaimer
This calculator is provided for educational and reference purposes only. It does not replace clinical judgment and should not be used to guide direct patient care. No warranty is made regarding accuracy; the operator assumes no liability for direct or indirect harm arising from use.
References: Nathan DM et al. Translating the A1C Assay Into Estimated Average Glucose Values. Diabetes Care. 2008;31(8):1473-1478. · American Diabetes Association. Standards of Care in Diabetes — 2024. Diabetes Care. 2024;47(Suppl 1).