Overnight time in range

Time in range is the proportion of a period during which glucose sits between 70 and 180 mg/dL. It comes from continuous glucose monitoring, so it can be read for any window: a day, a week, or a specific stretch of hours.

A1c is different. It reflects average glucose over roughly 90 days.

Two people can share an A1c and have had very different months, because averaging removes variability by design.

Here’s the clearest example. Someone who goes low at three in the morning and high by seven has two swings that partly cancel in an average. The A1c can look acceptable. The night wasn’t.

That is not a criticism of A1c, which does the job it was built for. It is a reason not to use it to answer a question about a specific window.

Luna Health’s analysis of a trial in adults with type 1 diabetes using insulin pumps estimates that evening-and-overnight closed-loop control delivers over 80% of the glycemic benefit of round-the-clock closed-loop control.¹

That is an analysis of one published study, not a result for Luna. What it implies is that the overnight window is not a small slice of the day's problem. It is where a large share of the available benefit sits.

It’s also the window when you’re asleep and can’t respond, which is an unusual combination: highest value, lowest ability to act.

Research with healthcare professionals found that time in range is well established among endocrinologists but considerably less familiar in primary care.²

If you’re reading CGM reports and want one number for the overnight window, overnight time in range is the one that describes it. It sits alongside A1c rather than replacing it.

This page explains a measure. It is not guidance about treatment targets, which belong with a clinician.