The 36% Line: Are Your Glucose Swings Actually "Stable"?

Your CGM app shows a number called coefficient of variation, usually written as CV and given as a percentage. Most people scroll past it. It's one of the most useful numbers on the screen, and it answers a question time in range can't: are your glucose swings actually steady, or just averaging out to something that looks fine?

What CV actually measures

Coefficient of variation describes how much your glucose bounces around its own average. Two people can average the same glucose, one riding gentle waves and the other lurching between highs and lows, and CV is the number that tells them apart. Low CV means steady. High CV means volatile, even if the average looks respectable.

That makes it different from time in range and different from A1C. Time in range tells you how many hours you spent in the target zone. CV tells you how turbulent the ride was inside and outside that zone.

The 36% threshold, read correctly

The international CGM consensus set the line at CV of 36% or below for stable glucose (Battelino 2019). Above 36%, glucose is considered unstable, and the risk of lows in particular climbs (Kovatchev 2016).

Here's the part people get wrong, and it's worth being exact about. 36% is a threshold you want to stay under. It is not a "36% improvement" and not a reduction you achieve. If your CV reads 33%, you're on the stable side of the line. If it reads 41%, your glucose is swinging more than the target allows. Think of it like a speed limit rather than a discount code: the goal is to be under the number, not to hit it.

Why it matters on a GLP-1

GLP-1 drugs work by flattening post-meal spikes, and spikes are a big contributor to a high CV. So CV is one of the clearest places to watch a GLP-1 do its job over time. If your CV drifts from the unstable side toward and under 36% while you're on the drug, that's steadiness you can see, not just an average that happens to land in a good spot.

One caution for readers without diabetes: the 36% cut-point comes from diabetes research, and the drug's variability numbers come from type 2 diabetes trials. Treat the threshold as a useful reference and watch your own CV trend rather than expecting a guaranteed change.

How to find and read yours

Open your CGM summary and look for "coefficient of variation" or "CV," usually near time in range. Check whether you're above or below 36%, then watch the trend across weeks rather than obsessing over a single day. A CV that's slowly falling and sitting under 36% is a steadier glucose profile. A CV that keeps climbing, especially alongside more time below range, is worth raising with your clinician.