Time in range is the percentage of your day that your blood sugar stays between 70 and 180 mg/dL. For most people with diabetes, the goal is to spend at least 70% of the day in that window, which works out to roughly 17 out of every 24 hours. It has become one of the most practical ways to evaluate blood sugar control, especially for anyone using a continuous glucose monitor (CGM).
Why Time in Range Matters More Than a Single Number
For decades, the A1c test was the gold standard for measuring diabetes management. A1c gives you a three-month average of blood sugar levels, but averages can be misleading. Someone whose blood sugar swings between 50 and 300 mg/dL multiple times a day could have the same A1c as someone who stays steadily between 100 and 160. Their day-to-day experience, and their risk of complications, are very different.
Time in range captures what an average cannot: stability. It tells you how much of your day your blood sugar is actually in a healthy zone, and equally important, how much time you’re spending dangerously high or dangerously low. That extra detail makes it far more useful for spotting patterns and adjusting your routine.
How Time in Range Connects to A1c
The two metrics aren’t competing. They correlate strongly. Research on people with Type 1 diabetes found a clear linear relationship between time in range and A1c. Roughly speaking, every 5 to 6 percentage-point increase in time in range corresponds to about a 0.5% drop in A1c. So moving from 53% time in range to about 59% would be similar to lowering your A1c from 7.5% to 7.0%.
The practical value of time in range is that it updates in real time. Rather than waiting three months for a lab result, you can see your time in range on a weekly or even daily basis and make adjustments to meals, activity, or medication timing right away.
The Three Zones on a CGM Report
Most CGM reports break your readings into three categories:
- Time in range (70 to 180 mg/dL): the target zone. Aim for 70% or more of your readings here.
- Time above range (over 180 mg/dL): periods of high blood sugar. Spending too much time here raises the risk of long-term complications like nerve damage and kidney disease.
- Time below range (under 70 mg/dL): periods of low blood sugar, or hypoglycemia. The general target is to spend less than 4% of the day below 70 mg/dL. Readings below 54 mg/dL are considered serious and should be as close to 0% as possible.
All three zones matter together. Improving your time in range is only beneficial if you’re not doing it at the cost of more lows. That’s why CGM reports show all three percentages side by side.
What the Research Shows About Complications
Time in range isn’t just a convenient metric. It has a direct relationship with the complications that make diabetes dangerous over time. A systematic review published in BMJ Open Diabetes Research & Care found that every 10% increase in time in range was associated with a measurable reduction in diabetic eye disease severity, kidney damage (measured by protein in the urine), and nerve damage including both peripheral neuropathy and cardiac autonomic neuropathy.
In practical terms, that means going from 50% time in range to 60% isn’t just a number on a screen. It represents a meaningful reduction in the likelihood of the complications most people with diabetes worry about. Those incremental improvements add up over months and years.
Different Targets for Different People
The 70% target applies to most adults with Type 1 or Type 2 diabetes, but not everyone has the same goal.
Pregnancy
Pregnant women with pre-existing diabetes need much tighter control. The American College of Obstetricians and Gynecologists recommends fasting blood sugar below 95 mg/dL, below 140 one hour after eating, and below 120 two hours after eating, with an A1c no higher than 6%. When translated to CGM metrics, this means spending more time in a narrower range, typically 63 to 140 mg/dL, with a time-in-range target closer to 70% or higher within that tighter window.
Older Adults
For healthy older adults with few other medical conditions and normal cognitive function, the standard 70% target still applies, with time below range kept under 4%. But for older adults managing multiple chronic conditions, cognitive decline, or limited mobility, the goals shift. A time in range of around 50% with time below range under 1% is considered appropriate. The priority becomes avoiding dangerous lows rather than chasing tight control, because hypoglycemia in a frail older person can lead to falls, confusion, and hospitalization.
For those with very complex health or end-stage illness, strict glucose targets offer little benefit. The focus shifts entirely to preventing symptoms: avoiding blood sugar levels low enough to cause confusion or high enough to cause excessive thirst and urination.
How to Improve Your Time in Range
If your time in range is below 70%, the first step is identifying when you leave the target zone. Most CGM apps show your daily glucose pattern overlaid across multiple days, making it easy to spot recurring spikes or dips.
Post-meal spikes are the most common reason for high time above range. The size and timing of carbohydrate intake, physical activity after eating, and the timing of any insulin or medication all influence how high your blood sugar climbs after a meal. Even a 10 to 15 minute walk after eating can noticeably blunt a post-meal spike.
Overnight lows are a common driver of time below range, particularly for people on insulin. If your CGM shows you regularly dropping below 70 mg/dL between 2 and 5 a.m., that’s a pattern worth discussing with your care team, as it often points to a medication timing or dosing issue.
Small, consistent changes tend to produce better results than dramatic overhauls. Moving from 50% to 60% time in range is a clinically meaningful improvement, and most people find that once they start watching the patterns, the adjustments become intuitive: a smaller portion of rice at dinner, a short walk after lunch, a bedtime snack on days with more physical activity. Each of those shifts pushes more of your day into the 70 to 180 zone, and the cumulative effect on long-term health is significant.