Continuous Glucose Monitor Calculator

A continuous glucose monitor's 14-day report boils down to a handful of headline numbers, and this calculator reproduces the standard ones defined by the International Consensus on Time in Range, published by Battelino and colleagues in Diabetes Care in 2019 and endorsed by eight international diabetes associations. Time in Range (70-180 mg/dL) is the single most emphasized metric, with a target of 70% or more of readings falling in that band; Time Below Range (under 70 mg/dL) is tracked separately because hypoglycemia carries outsized clinical risk even at a low overall percentage, with a target under 4%. The consensus guidance also sets a stricter target for the more severe end of that range -- under 1% of readings below 54 mg/dL -- since even brief severe hypoglycemia carries outsized risk; this calculator's single Time Below Range input covers the whole under-70 band and does not separately collect a below-54 count, so check that sub-threshold against the raw CGM report rather than this calculator's output.

From mean glucose, the calculator derives two different A1c-style estimates: the Glucose Management Indicator (GMI), a lab-independent formula (3.31 + 0.02392 x mean glucose) introduced by Bergenstal and colleagues in a 2018 Diabetes Care paper that intentionally does not try to replicate a lab A1c's biology, and a separate ADAG-formula estimated A1c ((mean glucose + 46.7) / 28.7) based on a different published calibration study -- the two can and often do disagree by a few tenths of a percent for the same mean glucose, which is expected rather than an error. Glycemic variability is measured as the coefficient of variation (glucose standard deviation divided by mean, as a percentage), with 36% as the commonly cited cutoff between stable and unstable glucose patterns. Finally, an overall composite score combines Time in Range, a heavy penalty for time spent below range, and a bonus for low variability into a single 0-100 number meant to give a quick orientation, not to replace looking at the individual metrics that feed it.