Health July 13, 2026 · 8 Min Read

A1C Calculator – Guide & Formulas

Convert between your Glycated Hemoglobin (HbA1c) percentage and Estimated Average Glucose (eAG) in mg/dL and mmol/L to monitor long-term diabetes control.

The A1C Calculator helps you convert between your HbA1c (Glycated Hemoglobin) percentage and your Estimated Average Glucose (eAG). HbA1c represents your average blood glucose over the past 2 to 3 months. This tool translates this laboratory percentage into the daily blood glucose metrics you measure on home monitors.

Key Takeaway

Use the free A1C Calculator to convert between your glycated hemoglobin (hba1c) percentage and estimated average glucose (eag) in mg/dl and mmol/l to monitor long-term diabetes control. Get instant results with step-by-step explanations.

How to Use the A1C Calculator

  1. Choose your conversion direction: HbA1c to eAG, or eAG to HbA1c.
  2. Enter your known percentage or average glucose reading.
  3. Check the converted value in both mg/dL and mmol/L.
  4. Examine the diabetes management diagnostic categories (Normal, Pre-diabetes, Diabetes) to assess glycemic control.

The Formula

eAG (mg/dL) = (28.7 * HbA1c) - 46.7 | eAG (mmol/L) = ((28.7 * HbA1c) - 46.7) / 18.0182

Variable Definitions

  • HbA1c: Glycated hemoglobin percentage, representing average blood glucose over red blood cell lifespans (120 days)
  • eAG: Estimated Average Glucose, comparable to daily self-monitoring glucose numbers

Translating a 7% A1C reading to eAG

A diabetes checkup reveals an HbA1c of 7.0%.

  1. Step 1: Set HbA1c = 7.0.
  2. Step 2: Multiply by 28.7: 7.0 * 28.7 = 200.9.
  3. Step 3: Subtract 46.7: 200.9 - 46.7 = 154.2 mg/dL.
  4. Step 4: Divide by 18.0182 to find mmol/L: 154.2 / 18.0182 ≈ 8.6 mmol/L.
  5. Step 5: A 7.0% A1C (154 mg/dL eAG) indicates controlled but active diabetes (target for most diabetic patients is < 7.0%).

Frequently Asked Questions

What are diagnostic A1C thresholds for diabetes?

Normal: Below 5.7%. Pre-diabetes: 5.7% to 6.4%. Diabetes: 6.5% or higher on two separate tests. For individuals already managing diabetes, a target below 7.0% is often recommended to minimize long-term vascular complications.

Why is A1C an average of the past 2 to 3 months?

Glucose sticks to hemoglobin (the oxygen-carrying protein in red blood cells) in a process called glycation. Because red blood cells live for about 120 days, measuring the percentage of glycated hemoglobin provides a reliable historical average of blood glucose concentrations.