CGM Metrics Calculator — GMI, Time in Range & Variability

Methodology

This tool computes the four standardised continuous-glucose-monitoring (CGM) metrics from the international consensus, entirely in your browser:

• Mean glucose — the simple average of your readings.
• Glucose Management Indicator (GMI) — an estimate of HbA1c from CGM data: GMI(%) = 3.31 + 0.02392 × mean glucose (mg/dL) (Bergenstal et al., Diabetes Care 2018). Readings in mmol/L are converted to mg/dL first (× 18.0182).
• Glucose variability (%CV) — standard deviation ÷ mean × 100. The consensus stability target is below 36%.
• Time in range (TIR) — the percentage of readings between 3.9 and 10.0 mmol/L (70–180 mg/dL), the consensus target range (Battelino et al., Diabetes Care 2019). We also show time below and above range.

Paste your readings (one per line, or comma-separated; rows like timestamp, glucose work too — we take the glucose value from each line).

Interpreting your result

For people managing diabetes, these are the numbers clinicians actually use: a common target is at least 70% time in range with %CV below 36%, and GMI gives a CGM-based estimate of HbA1c between lab tests. Two averages that look identical can hide very different variability, which is why %CV sits next to the mean.

If you don’t have diabetes, read this carefully. These metrics were developed for diabetes care. The popular idea that healthy people should chase a “flat” glucose line is not well supported — there is limited evidence that flattening normal post-meal rises in a metabolically healthy person improves health outcomes. Minor spikes after meals are normal physiology. Use these numbers as interesting self-tracking data, not as a diagnosis or a target to optimise anxiously.

Limitations

• GMI is an estimate of HbA1c from glucose, not a lab measurement; the two can differ, especially with conditions affecting red blood cells.
• Metrics are only as good as the data: short recording windows, sensor warm-up artefacts and compression lows can distort them.
• Targets (time-in-range goals, acceptable variability) are individual and set with a clinician — this tool reports the numbers, it does not prescribe goals.
• This is educational self-tracking, not a medical test. Anything concerning belongs with your doctor.

Sources

Pull the receipts — 2 cited sources

FitTools · sources

1. 01 Bergenstal RM, et al. Glucose Management Indicator (GMI): a new term for estimating A1C from CGM. Diabetes Care 2018;41:2275–2280
2. 02 Battelino T, et al. Clinical targets for continuous glucose monitoring data interpretation: recommendations from the international consensus on time in range. Diabetes Care 2019;42:1593–1603

Every formula cited ✓