Time in range (TIR) is the percentage of the day your blood sugar stays between 70 and 180 mg/dL (3.9 to 10.0 mmol/L). Most people with type 1 or type 2 diabetes should aim for at least 70% of readings in that window, which works out to roughly 17 out of every 24 hours. It’s measured by a continuous glucose monitor (CGM) and has become one of the most useful ways to understand day-to-day blood sugar control.
Why TIR Matters Beyond A1c
A1c has been the standard measure of blood sugar control for decades, but it only gives you an average over two to three months. Two people can have the same A1c while having very different daily experiences: one staying relatively steady, the other swinging between highs and lows that cancel each other out. TIR fills that gap by showing how stable your glucose actually is throughout the day.
The two metrics do correspond roughly. A TIR of 70% lines up with an A1c of about 7%, and a TIR of 80% corresponds to an A1c of roughly 6.4%. But the relationship isn’t exact. Someone with a TIR of 50% could have an A1c anywhere from 6.6% to 9.2%, depending on the pattern of their highs and lows. That wide spread is precisely why TIR adds information A1c can’t provide on its own.
The Five Glucose Zones on a CGM Report
Your CGM report breaks your glucose data into five categories, each with its own target:
- Very high (above 250 mg/dL): Less than 5% of readings
- High (181 to 250 mg/dL): Less than 25% of readings
- In range (70 to 180 mg/dL): At least 70% of readings
- Low (54 to 69 mg/dL): Less than 4% of readings
- Very low (below 54 mg/dL): Less than 1% of readings
The time below range targets are especially important. Spending more than 4% of the day with low blood sugar (about an hour) signals a real risk of dangerous hypoglycemia. The goal isn’t just to push your numbers down into range; it’s to do so without creating more lows.
How TIR Connects to Complications
Higher time in range is directly linked to lower risk of diabetes complications. A post hoc analysis of the landmark Diabetes Control and Complications Trial found that for every 10 percentage points TIR dropped, the risk of retinopathy (diabetes-related eye damage) progressing increased by 64%. The same analysis found a similar relationship with kidney damage. In other words, the difference between 70% and 60% TIR isn’t trivial. Each percentage point you gain offers measurable protection for your eyes, kidneys, and cardiovascular system over time.
Targets for Different Groups
The 70% target applies to most adults with type 1 or type 2 diabetes, but not everyone. Your targets may be adjusted based on age, pregnancy status, or complication risk.
Older Adults and High-Risk Individuals
For people over 60 or those at high risk of hypoglycemia (including anyone with hypoglycemia unawareness, where you can’t feel your blood sugar dropping), the recommended target drops to greater than 50% TIR, or about 12 hours per day. This more relaxed goal reflects the fact that severe lows are especially dangerous in older adults. For people with existing heart or blood vessel complications, the lower boundary of the range is sometimes raised to 79 mg/dL (4.4 mmol/L) to provide an extra buffer against hypoglycemia.
Pregnancy
Pregnant women with type 1 diabetes use a tighter glucose window of 63 to 140 mg/dL (3.5 to 7.8 mmol/L). To reach the pregnancy A1c goal of under 6.0%, research shows they need to spend at least 78% of the day in that tighter range, about 18 hours and 43 minutes. The stakes are higher because even moderately elevated blood sugar during pregnancy affects fetal development.
How TIR Is Measured
You need a CGM to get a meaningful TIR reading. These small sensors sit just under the skin and take a glucose reading every one to five minutes, generating hundreds of data points per day. The data is compiled into a standardized report called an Ambulatory Glucose Profile (AGP), which your healthcare provider can review at appointments.
For TIR data to be reliable, you generally need at least 14 days of CGM wear with the sensor active for at least 70% of the time. Shorter windows can be skewed by a single unusual day.
Your CGM report also calculates a number called the Glucose Management Indicator (GMI). This uses your average CGM glucose over 14 or more days to estimate what your lab A1c would likely be, using the formula: GMI (%) = 3.31 + 0.02392 × mean glucose in mg/dL. It’s useful as a real-time check between quarterly lab draws, though it can diverge from your actual A1c because of individual differences in how red blood cells process sugar.
Practical Ways to Improve Your TIR
Because CGM data updates continuously, you can see in real time what pushes you out of range. Most people discover a few consistent patterns: a post-meal spike from a specific food, a dawn phenomenon that raises fasting glucose, or a drop after exercise. Identifying those patterns is the first step toward changing them.
Small changes tend to compound. Eating protein or fat before carbohydrates in a meal can blunt the post-meal spike. A 10-to-15-minute walk after eating does the same. Timing medications differently, or adjusting insulin doses with guidance from your provider, can target the specific windows where you’re spending the most time above range. The CGM essentially turns blood sugar management from a guessing game into a feedback loop, where you can test a change and see the result within hours.
It’s also worth keeping perspective. Even well-managed diabetes involves some time outside the target range. The 70% goal means it’s expected and completely normal to be above 180 mg/dL or below 70 mg/dL for portions of the day. Perfection isn’t the standard. Consistency is.