Time in Range Calculator
CGM time in range, time below and above range, and the GMI estimate from your mean glucose.
What it does
A1C tells you the average, but it hides the ride. Two people with the same A1C can spend wildly different shares of the day high or low, and time in range makes that visible by counting minutes in the zones that matter: 70 to 180 mg/dL in range, below 70 low, below 54 very low, above 180 high, above 250 very high.
The tool above turns your CGM zone minutes into the four standard percentages, then computes the glucose management indicator, a formula that converts your mean sensor glucose into the A1C number your sensor data is roughly equivalent to.
The defaults describe a fairly typical day: 1,005 of 1,440 minutes in range with a mean glucose of 154 mg/dL. That reads 69.8 % in range, 3.1 % below, 27.1 % above, and a GMI of 7.0 %. The metric mirror at 8.6 mmol/L produces identical percentages and adds the molar-unit version of the estimate, about 53.18 mmol/mol.
The zone boundaries and target percentages follow the international consensus on CGM metrics and the ADA Standards of Care, which recommend judging these numbers over at least 14 days of wear. The GMI formula comes from the published CGM analysis derived from thousands of paired sensor and lab readings.
How to use
- Pick US or metric units for the mean glucose.
- Enter the mean sensor glucose from your CGM report.
- Fill in the minutes recorded in each of the five zones.
- Leave 0 for any zone with no time; partial days still work.
- Read time in range first, then below and above, then the GMI.
Formula
- TIR
- Percent of recorded minutes between 70 and 180 mg/dL.
- mean glucose
- Average sensor glucose, in mg/dL for the GMI formula.
- GMI
- Glucose management indicator, an A1C-style percentage estimated from the mean.
- mmol/mol
- Molar-unit A1C, estimated as 12.71 + 4.70587 x mean glucose in mmol/L.
Percentages here divide by the minutes you actually entered, not a fixed 1,440, so a partial day or a sensor gap still produces usable shares; the note under the result says when the total is not a full day. The GMI formula was fitted on CGM data paired with lab A1C, so it estimates what a lab might show for that average, and individual results scatter around it. It is a summary of the mean only: two identical GMI values can come from a steady line or a roller coaster, which is why time in range and the low percentage carry their own targets.
Worked example
Example: 154 mg/dL average with a mostly steady day
Defaults: 15 minutes very low, 30 low, 1,005 in range, 330 high, 60 very high, mean 154 mg/dL.
- Total recorded: 15 + 30 + 1,005 + 330 + 60 = 1,440 minutes.
- TIR: 1,005 / 1,440 = 69.8 %.
- Below range: 45 / 1,440 = 3.1 %, of which very low is 15 / 1,440 = 1.0 %.
- Above range: 390 / 1,440 = 27.1 %.
- GMI: 3.31 + 0.02392 x 154 = 6.99, shown as 7.0 %.
Reference table
| Metric | Common goal | Defaults |
|---|---|---|
| Time in range (70 to 180) | Above 70 % | 69.8 % |
| Time below 70 | Under 4 % | 3.1 % |
| Time below 54 | Under 1 % | 1.0 % |
| Time above 180 | Under 25 % | 27.1 % |
| Time above 250 | Under 5 % | 4.2 % |
Limits
- Needs accurate zone minutes from your CGM report.
- GMI assumes a typically calibrated sensor; it is not a lab A1C.
- Does not measure glucose variability or overnight patterns.
- Targets differ in pregnancy and for older or high-risk adults.
Common mistakes
- Comparing a partial day of data against full-day targets.
- Changing insulin doses on a single day of numbers.
- Treating GMI as a replacement for a lab A1C.
- Chasing time in range while ignoring time below.
- Entering mmol/L values into the mg/dL field.
Try it yourself
Quick checks. Answers sit tucked under each question.
Mean glucose 183 mg/dL?
GMI lands near 7.7 %: 3.31 + 0.02392 x 183.
A full day, entirely in range, mean 120 mg/dL?
TIR 100 %, with a GMI of 6.2 %.
Metric user with a mean of 8.6 mmol/L?
Same percentages; GMI 7.0 %, about 53.18 mmol/mol.
Questions
What is time in range?
The share of the day your sensor glucose sits between 70 and 180 mg/dL, the band most adults with diabetes are asked to spend at least 70 % of the time inside.
What is a good TIR?
Above 70 % for most adults, with below 70 mg/dL under 4 % and below 54 mg/dL under 1 %. Higher is generally better while those low percentages stay small.
What is the GMI?
A formula that converts your mean sensor glucose into the A1C number that average corresponds to; it stands in for a lab result between visits, not instead of one.
How many days of data should I read?
At least 14 days, per the consensus guidance, because a single day swings with meals, exercise, and sleep.
My minutes do not add to 1,440. Is that a problem?
No. The tool divides by your actual total and tells you when that total is not a full day; sensor gaps and partial wear days are handled the same way.
Does better TIR mean better health?
Studies link more time in range with fewer complications, but targets are personal; your care team weighs your lows, age, and other conditions.
Sources
- ADA Standards of Care in Diabetes
- Battelino et al., Clinical targets for continuous glucose monitoring data interpretation (PMC6973648)
- Glucose management indicator: CGM metrics and A1C (PMC6196826)