What Is Time in Range (and Why an Average Isn't Enough)

Time in range asks a simple question that a single average can't answer: of all the hours in a day, how many did your glucose actually spend where you'd want it to be? It reframes blood sugar from one long-term number into a picture of the whole day — and for many people, that picture is where the useful detail lives.

What time in range means

Time in range (TIR) is the percentage of time your glucose stays within a target band. For many adults that band is defined as 70–180 mg/dL (about 3.9–10.0 mmol/L). It is measured with a continuous glucose monitor, which samples glucose every few minutes and can therefore calculate how much of the day fell inside, above, or below the target.

TIR usually comes with two companions that matter just as much:

• Time below range (TBR) — the share of time spent below the low threshold, which relates to the risk of hypoglycemia.
• Time above range (TAR) — the share spent above the high threshold, reflecting hyperglycemia.

Together these describe not just where your glucose averaged out, but how the day was actually spent.

The consensus targets

In 2019, an international group of experts published a consensus on CGM targets in the journal Diabetes Care, and these figures are referenced by organizations including the American Diabetes Association. For many non-pregnant adults with diabetes, the commonly cited goals are:

• More than 70% of time in range (70–180 mg/dL).
• Less than 4% of time below range (below 70 mg/dL), and less than 1% below 54 mg/dL.
• Less than 25% of time above range (above 180 mg/dL).

These are population-level reference points, not universal rules. The consensus itself notes that targets should be individualized — older adults, people at high risk of hypoglycemia, and pregnancy all have different recommended ranges. Your own goals should be set with a clinician who knows your history. You can get a rough sense of your own numbers with our time in range calculator.

Why the same HbA1c can hide two very different days

Imagine two people with an identical HbA1c. One holds a gentle, steady line most of the day. The other spikes high after meals and then drops low, and those swings happen to average out to the same number. On paper they look the same. In lived experience they are not — the second person spends far less time in range and more time both high and low.

This is the core reason an average alone can feel incomplete. TIR and its companions capture the shape of the day that a single value flattens. They sit alongside a related idea, glucose variability, which measures how wide those swings are. Neither replaces HbA1c; they add context to it.

How CGM measures it

Because a CGM records glucose continuously, software can add up exactly how many minutes fell inside the target band and express it as a percentage. Reports often summarize a two-week period, and a rough rule of thumb sometimes cited is that each 5% of time in range corresponds to about 1.2 hours a day. Clinicians generally like to see enough wear time — often around 70% of the period — before reading too much into the numbers, since a partial record can skew the picture.

How to think about your own number

If you use a CGM, TIR is best treated as a conversation starter rather than a scoreboard. A lower-than-hoped number is not a failure; it's a prompt to look at when glucose leaves the range — after certain meals, overnight, or during stress — and to discuss with a clinician whether anything should change. The goal for most people is gradual, sustainable improvement, not a perfect trace.

Sources

Further reading from established public sources: American Diabetes Association — CGM & Time in Range · Battelino et al., Diabetes Care (2019) — Clinical Targets for CGM Data Interpretation · NIH / NIDDK — Continuous Glucose Monitoring.

Related: HbA1c vs CGM · Glucose variability, explained · What is GMI