Gmi to A1c Calculator

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GMI to A1c Calculator

Estimate your Glucose Management Indicator from average glucose levels

mg/dL mmol/L

Calculation Results

GMI Value —%
Estimated Lab A1c —%

What is GMI (Glucose Management Indicator)?

The Glucose Management Indicator (GMI) is a metric used by Continuous Glucose Monitors (CGM) to estimate what your A1c is likely to be based on your average glucose readings over a specific period (usually 10 to 14 days). While lab-tested HbA1c measures the glucose attached to hemoglobin in red blood cells over 3 months, GMI is a mathematical calculation derived directly from sensor data.

How the Calculation Works

This calculator uses the standardized clinical formula to derive GMI from your average blood sugar. If you enter your data in mmol/L, it is first converted to mg/dL before the formula is applied.

  • GMI Formula: 3.31 + (0.02392 × Average Glucose in mg/dL)
  • Estimated A1c (eA1c) Formula: (Average Glucose in mg/dL + 46.7) / 28.7

GMI vs. HbA1c: Why are they different?

It is very common for your lab A1c and your CGM's GMI to differ. Factors such as red blood cell lifespan, iron deficiency, or pregnancy can affect lab A1c. GMI is often considered a more accurate reflection of recent management because it is calculated from thousands of data points provided by your CGM sensor.

Real-World Example

If your average glucose over the last 14 days was 154 mg/dL:

  1. GMI Calculation: 3.31 + (0.02392 × 154) = 7.0%
  2. eA1c Calculation: (154 + 46.7) / 28.7 = 7.0%

Note that while they match perfectly in this specific example, the formulas diverge slightly at higher and lower averages.

function calculateGMI() { var avgValue = parseFloat(document.getElementById('avgGlucose').value); var unit = document.getElementById('unitType').value; var resultDiv = document.getElementById('resultsWrapper'); var gmiSpan = document.getElementById('gmiResult'); var eA1cSpan = document.getElementById('eA1cResult'); var interpretationPara = document.getElementById('interpretation'); if (isNaN(avgValue) || avgValue <= 0) { alert("Please enter a valid average glucose number."); return; } var mgdlValue = avgValue; if (unit === 'mmoll') { mgdlValue = avgValue * 18.0182; } // Formula: GMI (%) = 3.31 + 0.02392 * [mean glucose in mg/dL] var gmi = 3.31 + (0.02392 * mgdlValue); // Formula: eA1c = (Average Glucose + 46.7) / 28.7 var ea1c = (mgdlValue + 46.7) / 28.7; gmiSpan.innerHTML = gmi.toFixed(1); eA1cSpan.innerHTML = ea1c.toFixed(1); resultDiv.style.display = 'block'; var status = ""; if (gmi = 5.7 && gmi < 6.5) { status = "Your estimated levels are within the pre-diabetic range."; } else { status = "Your estimated levels indicate management consistent with diabetes guidelines."; } interpretationPara.innerHTML = "Interpretation: " + status + " Always consult with your healthcare provider for medical diagnosis and treatment decisions."; }

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