Time in range explained
What the percentage on your sensor measures, and why it treats your day as a whole rather than judging one reading.
Time in range is the share of the day your glucose sits inside your target band, usually shown as a percentage on your sensor or app. It’s a way of seeing your days as a whole, rather than judging one reading at a time.
- Time in range means the percentage of the day (24 hours) your glucose stayed inside your target band, not a single moment.
- The band isn’t one number: NHS targets vary by time of day, roughly 5-7 mmol/L on waking, 4-7 before meals, 5-9 after, and your team may set yours differently.
- A common shared goal is around 70% of the day in range, but the number that fits you is one to agree with your team, not a pass mark.
- It works alongside HbA1c (your rough three-month average), showing the ups and downs a single average hides.
- You only see it if you use a sensor that reads glucose through the day, not finger-prick checks alone.
What it tells you that a single number can’t
HbA1c gives you an average over about three months. The trouble with an average is that two very different days can produce the same one. Lots of highs cancelled out by lots of lows can average to something that looks fine, while you’ve actually been on a rollercoaster.
Time in range shows the shape of your days instead. It splits your glucose into time spent below range (lows), in range, and above range (highs), so you can see whether the problem is mostly one direction or both. That’s the difference between “your average is 8” and “you spend most evenings running high and most nights dipping low”, which point at completely different things to look at.
What it changes day to day
Because time in range updates as the day goes, it can show you patterns tied to specific moments: the hours after breakfast, the gap before your evening meal, the night. That’s more useful than a three-monthly number when you’re trying to work out what’s actually happening.
The honest caveat is that the percentage moves with your habits, your sensor wear, illness, stress and plenty else. One low week doesn’t mean something’s gone wrong, and one high week isn’t a verdict. It’s a pattern to read, not a score to hit. If a stretch of days looks different from usual, the question is what changed, not what you did wrong.
Turning the pattern into something you’d do
The point of seeing a pattern is to have something specific to raise or try, not just to know it’s there. If your sensor shows you climb high most mornings after breakfast, that’s a concrete thing to take to your team: it might be about the timing of your mealtime insulin, or the type of breakfast, and they can help you work out which.
Small, testable changes are the way in. If breakfast sends you high, one thing people try is swapping white toast or a sugary cereal for porridge or eggs for a week, then looking at whether those morning hours flatten out. That’s a food change you can watch, not a dose change, and anything dose-shaped goes to your team first.
What moves time in range
Your target band itself changes through the day, so “in range” at 3pm isn’t the same number as “in range” at 7am. On top of that, food, insulin timing, illness and stress all push glucose around.
Activity is the one people most often read wrong. Steady, moderate movement (a walk, a swim, a gentle cycle) tends to lower glucose. But hard, intense effort (sprints, heavy lifting, a competitive match) can push it up in the moment, because of the stress hormones involved. And exercise lows aren’t always at the time: activity can drop your glucose hours later, including overnight, as your muscles refill their fuel stores. So a session can pull your time in range in either direction, and the effect can land long after you’ve stopped.
How it reads
Examples, not instructions or doses.
Your sensor shows you sitting around 5-6 mmol/L overnight, then climbing to 11-12 for two or three hours after breakfast most days. In range overnight, out of range every morning. That’s a pattern pointing at breakfast, worth raising with your team.
Your HbA1c looks steady, but time in range shows you spend a chunk of most afternoons above 10 and a chunk of most nights below 4. The average is calm; the days aren’t. The lows are the part to flag first.
You played hard at 7pm, felt fine, went to bed at 8 mmol/L. Your sensor shows a dip below 4 at 2am. The intense game masked the drop that came hours later, which is common and worth planning around.