How to Choose a CGM: What to Know Before You Buy One
What actually differs between them, what the subscriptions cost, and the question worth asking before buying one at all.
Over-the-counter sensors have made this a consumer purchase. Here's what actually varies, and the prior question.
The prior question: do you need one?
Worth asking, because the answer is often no.
A CGM is most useful if you want to understand your own responses to specific foods, you've had confusing test results, or you're motivated by data and will act on it.
It's least useful if you already know what to do and aren't doing it. A sensor won't tell you anything you don't know about the cookie.
It's actively unhelpful if you have a history of disordered eating or find yourself anxious about food. Clinicians have specifically raised concerns that glucose self-monitoring can drive restriction, and a device that scores every meal is a poor fit for that.
Two weeks of deliberate experiments is usually worth more than a permanent subscription.
What actually differs between devices
Wear time. Sensors typically run 10–15 days.
Warm-up period. Usually the first hour or two, and readings in the first 24 hours are generally least reliable regardless of brand.
Accuracy. Broadly comparable across current consumer sensors, with meaningful variation between individual sensors. All measure interstitial fluid, which lags blood glucose by roughly 5–10 minutes.
App quality. Genuinely variable, and it matters more than people expect — how easily you can log meals, view patterns and export data.
Alarms. Some consumer versions restrict or remove low-glucose alerts, which matters more for some users than others.
Subscription model. This is where the cost sits. Sensors are consumable, so the ongoing cost dwarfs the initial purchase.
On cost
Prices and availability change frequently enough that any figure here would date. The relevant question is the monthly cost rather than the sensor cost, and whether you plan to wear one continuously or for defined periods.
Two two-week periods a year costs a fraction of continuous wear and, for most people without diabetes, provides most of the value.
If you have diabetes
Different conversation entirely. Ask your clinician whether you qualify for a prescribed CGM — funding criteria have expanded in many places, and the prescribed devices are integrated with clinical care in a way consumer ones aren't.
Don't buy one over the counter before asking whether you can get one through your care.
How to actually use it
Experiments, not surveillance. One variable at a time, held for three days. The same breakfast with and without added protein tells you something. Watching every reading tells you very little and costs a great deal of attention.
Try this week: if you're considering one, write down the three questions you want it to answer. If you can't name three, you probably don't need it yet.
Education, not medical advice. If you have diabetes, discuss monitoring with your care team.