If you live with diabetes, you've probably had your A1C checked dozens — maybe hundreds — of times. It's the number your endocrinologist watches. The number insurance companies use. The number that, for better or worse, has defined what "good management" looks like for over 30 years.
But A1C is an average. And averages hide a lot.
Two people can have the same A1C of 7.0% and have completely different daily experiences — one with stable glucose throughout the day, the other swinging between dangerous lows and exhausting highs. A1C can't tell the difference.
Time in Range can.
Time in Range (TIR) measures the percentage of time your glucose stays within a target zone — typically 70 to 180 mg/dL (3.9 to 10.0 mmol/L) for most adults with Type 1 or Type 2 diabetes.
If your TIR is 70%, that means your glucose was within that target zone for about 16 hours and 48 minutes out of every 24-hour day. The remaining 30% — roughly 7 hours — was spent above or below the target.
Unlike A1C, which gives you a single number reflecting a two-to-three-month average, TIR shows you when and how often things go off track. It reveals patterns that most of us can't.
In 2019, an international panel of clinicians and researchers published what has become the standard framework for TIR goals. Known as the ATTD Consensus, the targets are straightforward:
| Metric | Target | What It Means |
|---|---|---|
| Time in Range (70–180 mg/dL) | >70% | More than ~17 hours/day in target |
| Time Below Range (<70 mg/dL) | <4% | Less than ~1 hour/day below target |
| Time Significantly Below (<54 mg/dL) | <1% | Less than ~15 minutes/day |
| Time Above Range (>180 mg/dL) | <25% | Less than ~6 hours/day above target |
| Time Significantly Above (>250 mg/dL) | <5% | Less than ~1 hour and 12 minutes/day |
These aren't arbitrary. Research published in Diabetes Care found that for every 10% decrease in TIR, the risk of diabetic eye disease increases by 64%, and the risk of early kidney damage increases by 40% (Beck et al., 2019). Every percentage point matters.
The consensus also notes that each 5% improvement in TIR — about 72 additional minutes per day in range — is considered clinically meaningful. You don't have to reach 70% overnight. Progress in any direction counts.
For pregnant individuals with diabetes, the targets are tighter: 63–140 mg/dL with a goal of >70% TIR in that narrower range.
A1C and TIR aren't enemies — they measure different things. Think of A1C as your semester GPA and TIR as your individual test scores. The GPA tells you the overall trend. The test scores show you where you're thriving and where you're struggling.
Here's where they diverge:
A1C is a weighted average. It reflects red blood cell glucose exposure over 2–3 months, but it's heavily influenced by recent weeks and doesn't distinguish between stable glucose and wide swings. A study by Vigersky and McMahon (2019) found that a 10% increase in TIR corresponds to roughly a 0.8% decrease in A1C — and that 70% TIR aligns approximately with a 7.0% A1C.
But that alignment breaks down at the individual level. Two people with identical A1Cs can have vastly different TIR profiles. One may spend most of their out-of-range time slightly above 180, while the other oscillates between severe lows and extreme highs. Their A1Cs look the same. Their daily lives — and their complication risks — do not.
This is why the American Diabetes Association's 2026 Standards of Care now recommends assessing glycemic status using both A1C and CGM-derived metrics, including TIR, time above range, and time below range. TIR isn't replacing A1C — it's completing the picture.
Most people check their glucose during the day, when they're making active decisions about food, insulin, and activity. But what happens during the 7–8 hours you're asleep?
For many insulin users — particularly those on pen therapy — nighttime is the hardest period to manage. Basal insulin provides a fixed dose that can't adapt to the body's changing needs overnight: the natural dip in insulin sensitivity in the early morning hours, the hormonal surges that drive glucose up before dawn, or the slow creep of a high that started before bed.
These patterns show up clearly in TIR data when you separate daytime from nighttime hours. And for many people, nighttime is where the biggest opportunities for improvement live.
If you've ever woken up frustrated by a morning glucose reading that didn't match what you did the night before, nighttime TIR helps explain why. It's not a failure of willpower. It's physiology — and it's the exact window where automated insulin delivery makes the most difference.
If you use a continuous glucose monitor (CGM), you likely already have access to TIR data:
Ambulatory Glucose Profile (AGP) reports. Most CGM platforms — Dexcom Clarity, LibreLink, Glooko — generate a standardized AGP report that shows your TIR breakdown. Your endocrinologist may pull this up during clinic visits, or you can access it yourself through the companion app.
14-day snapshots. The international consensus recommends a minimum of 14 days of CGM data with at least 70% active wear time to get a reliable TIR reading. Less than that, and the numbers may not reflect your true patterns.
Daily and weekly trends. Many CGM apps let you filter TIR by time of day — morning, afternoon, evening, and overnight. This is where the real insights live. A strong overall TIR with poor overnight numbers tells a very different story than the reverse.
If you don't use a CGM, your endocrinologist can estimate TIR from structured blood glucose logs, though the data will be less complete. If you're curious about your nighttime patterns specifically, even a short trial period with a CGM can be revealing.
Improving TIR doesn't require a complete overhaul. Small, consistent changes compound:
Start with the overnight window. For many people, nighttime glucose is both the most variable and the most improvable. Talk to your endocrinologist about basal insulin timing, dose adjustments, or whether nighttime automation might be appropriate.
Reduce post-meal spikes. Pre-bolusing (taking rapid-acting insulin 10–15 minutes before eating), choosing lower-glycemic foods, and walking after meals can meaningfully reduce time above 180 mg/dL.
Address lows first. Time below range is a safety priority. If your TBR is above 4%, work with your care team to reduce hypoglycemia before focusing on bringing down highs. Every episode of severe hypoglycemia has downstream effects on how confidently you manage the rest of your day.
Review your data weekly, not daily. TIR is most useful as a trend over days and weeks. Daily fluctuations are normal. What matters is whether the overall trajectory is moving in the right direction.
At Luna, we chose TIR as the primary endpoint in our pilot study — specifically, nighttime TIR improvement measured by a connected CGM. We believe TIR captures what matters most to the people we're building for: not just a lower number on a lab report, but more hours of stable glucose during the hours you're asleep and unable to intervene.
It's a metric that sees the full picture. And we think everyone living with diabetes deserves to see it too.