GMI & CGM Time-in-Range Calculator

About the GMI & CGM Time-in-Range Calculator

A continuous glucose monitor (CGM) records a reading every few minutes, and an international consensus defines the numbers that summarise them: time in range (70–180 mg/dL, 3.9–10.0 mmol/L), time below range (under 70 and under 54 mg/dL), time above range (over 180 and over 250 mg/dL), the coefficient of variation (CV) and the glucose management indicator (GMI), an HbA1c-like value worked out from the mean glucose.

Choose a CSV export from Dexcom Clarity or LibreView — or another CGM program, if its file has a time column and a glucose column — and the calculator reads it in your browser with PapaParse: the file is never uploaded. You get every consensus metric checked against the targets for your situation (type 1 or type 2 diabetes, older or high-risk adults, or pregnancy), a daily glucose profile of the median and spread of your readings by time of day, and a day-by-day table. No file? Enter a mean glucose to get the GMI alone, or try the made-up example data.

Without a pass, the free preview shows the time in range (or the GMI) in full with every warning, a watermarked daily profile and the first rows of each table; a Pro pass unlocks every metric, the whole tables, Copy summary and the CSV download.

Common uses

• Getting the consensus CGM metrics from an export before a diabetes appointment.
• Checking time below range and overnight lows across several weeks of sensor data.
• Comparing the last 14 days with the last 90 from the same file.
• Working out the GMI from a mean glucose and comparing it with a laboratory HbA1c.

The metrics and their targets

For most adults with type 1 or type 2 diabetes the international consensus sets:

• In range, 70–180 mg/dL (3.9–10.0 mmol/L): over 70% (about 16 hours 48 minutes a day)
• Below 70 mg/dL (3.9 mmol/L): under 4% (under 1 hour a day), and below 54 mg/dL (3.0 mmol/L): under 1% (under 15 minutes)
• Above 180 mg/dL (10.0 mmol/L): under 25% (under 6 hours), and above 250 mg/dL (13.9 mmol/L): under 5%
• Glucose variability (CV): 36% or less

For people under 25 whose HbA1c goal is 7.5%, the consensus suggests a time-in-range target of about 60%. For older people or those at high risk of hypoglycaemia: in range over 50%, below 70 mg/dL under 1% and above 250 mg/dL under 10%. In pregnancy with type 1 diabetes the range is 63–140 mg/dL (3.5–7.8 mmol/L): over 70% in range, under 4% below 63 mg/dL, under 1% below 54 mg/dL and under 25% above 140 mg/dL. For type 2 or gestational diabetes in pregnancy the consensus gives the same ranges but no percentage targets, because evidence is limited. For reliable figures it recommends 14 days of data with at least 70% of the possible readings.

The glucose management indicator (GMI)

GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL), and GMI (mmol/mol) = 12.71 + 4.70587 × mean glucose (mmol/L). It estimates the HbA1c expected from your CGM mean, and needs at least 10 and preferably 14 or more days of data. It is not the same as a laboratory HbA1c: in the study that defined it, the two were identical 19% of the time and differed by 0.5 percentage points or more 28% of the time. The equation was derived with one brand of sensor, and the ADA describes GMI as a calculated value approximating A1C that is not always equivalent to it.

What the calculator reads in your file

• Dexcom Clarity: the rows whose event type is EGV (the sensor readings); alerts, calibrations, insulin and carbohydrate rows are skipped and counted.
• LibreView: the historic glucose readings (record type 0); scans, strip tests, notes, food and insulin rows are skipped.
• Other programs: the first column named like a glucose value, beside a time column (or a date and a time column).
• Units come from the column name (mg/dL or mmol/L); a file without one is read by the size of its values, and you can change it.
• “Low” and “High” (readings outside the sensor’s range) count as very low or very high in the time in ranges and are left out of the mean, SD, CV, GMI and the profile.
• Duplicate times are counted once. Dates are read as written, without any time-zone change.

Reading the daily profile

The profile stacks every day of the period on one 24-hour axis, as the ambulatory glucose profile (AGP) report does. The line is the median reading at each time of day; the dark band holds the middle half of readings (25th to 75th percentile) and the light band 90% of them (5th to 95th). A band that rises above the target range after a meal, or dips below it at night, shows a pattern that repeats from day to day, which is easier to act on with your diabetes team than any single reading.

Sources

• Battelino T et al. Clinical targets for continuous glucose monitoring data interpretation: recommendations from the international consensus on time in range — Diabetes Care, Tables 2–4
• Bergenstal RM et al. Glucose Management Indicator (GMI): a new term for estimating A1C from continuous glucose monitoring — Diabetes Care
• American Diabetes Association. Glycemic Goals, Hypoglycemia, and Hyperglycemic Crises: Standards of Care in Diabetes — Recommendations 6.3b and 6.3c, Table 6.2
• PapaParse — the CSV reader that runs in your browser

Limitations

• A summary of your own data, for information — not a diagnosis and not advice on insulin or other treatment.
• Reads the readings and times in the file as they are. Sensor errors, warm-up periods and gaps in wear are not corrected.
• The consensus targets apply to people with diabetes; they are not targets for people without diabetes.
• Files up to 25 MB; very large exports may take a few seconds to read on older phones.

Privacy

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