Continuous Glucose Monitor Calculator

CGM data interpretation: time in range and GMI.

Medical Disclaimer

This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.

Inputs

Mean Glucose (mg/dL)

Glucose SD (mg/dL)

Time in Range 70–180 (%)

Time Below Range <70 (%)

Tab to move between fields

Results

GMI (%)

6.99

Estimated A1c (%)6.99

Coefficient of Variation (%)26

Time Above Range >180 (%)27

Variability Rating (0–2)0

CGM Score (0–100)65

How to Use This Calculator

Enter Mean Glucose (mg/dL) and Glucose Standard Deviation from the CGM report.
Input Time in Range 70-180 % and Time Below Range < 70 %.
Enter Glucose Management Indicator (GMI) from the device software.
Review Estimated A1c, Coefficient of Variation (CV), and Variability Rating.
A CV below 36% and Time in Range above 70% indicate stable glucose management.

How the result changes with Mean Glucose (mg/dL)

Mean Glucose (mg/dL)	GMI (%)
86	5.37
201	8.12
339	11.42
454	14.17

What each input means

Mean Glucose (mg/dL): Average glucose reading from CGM over the reporting period (typically 14 days).
Glucose SD (mg/dL): Standard deviation of glucose readings. Used to calculate coefficient of variation.
Time in Range 70–180 (%): Percentage of time glucose is between 70–180 mg/dL. Target ≥70%.
Time Below Range <70 (%): Percentage of time glucose is below 70 mg/dL. Target <4%.

What each result means

GMI (%): Glucose Management Indicator — lab-independent A1c estimate: 3.31 + 0.02392 × mean glucose.
Estimated A1c (%): Estimated HbA1c from mean glucose using ADAG formula: (mean + 46.7) / 28.7.
Coefficient of Variation (%): Glycemic variability index. Target <36% for stable glucose. ≥36% = high variability.
Time Above Range >180 (%): Percentage of time glucose is above 180 mg/dL. Target <25%.
Variability Rating (0–2): 0 = Stable (CV <36%), 1 = Moderate (36–50%), 2 = High variability (>50%).
CGM Score (0–100): Composite score based on TIR, hypoglycemia penalty, and variability bonus. Higher is better.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Mean Glucose (mg/dL) = 154, Glucose SD (mg/dL) = 40, Time in Range 70–180 (%) = 70, Time Below Range <70 (%) = 3 = 4 input(s) provided
Calculate GMI
GMI = 3.31 + 0.02392 * meanGlucose
6.99 = 6.99
Calculate Estimated A1c
Estimated A1c = (meanGlucose + 46.7) / 28.7
6.99 = 6.99
Calculate Coefficient of Variation
26 = 26