Dexcom continuous glucose monitors take a new glucose reading every 5 minutes, automatically and around the clock. That adds up to as many as 288 readings per day (Dexcom’s own materials cite up to 244, accounting for brief gaps during signal loss or sensor changes). No scanning, no finger pricks, and no manual input needed for each reading.
How the 5-Minute Reading Works
A Dexcom sensor is a tiny filament that sits just under the skin, resting in the interstitial fluid (the thin layer of fluid between your cells). Every 5 minutes, the sensor measures the glucose concentration in that fluid and wirelessly sends the number to your phone app or a standalone receiver. The readings appear as a continuous trend line on your screen, so you’re not just seeing a single snapshot but a moving picture of where your glucose has been and where it’s heading.
One thing worth knowing: the sensor isn’t measuring blood directly. Because it reads interstitial fluid, there’s a slight delay compared to what a traditional fingerstick would show. That lag can be up to 15 minutes but is typically less. You’ll notice it most when your glucose is changing fast, like right after a meal or during intense exercise. During stable periods, the sensor and a fingerstick will track closely together.
Accuracy of Those Readings
Dexcom quantifies accuracy using a metric called MARD (mean absolute relative difference), which is essentially the average percentage a sensor reading deviates from a lab-grade blood test. The G7 has a MARD of about 9.8%, meaning on average it’s within roughly 10% of a lab value. The older G6 comes in around 11.2%.
Accuracy also improves over the life of a sensor. On day one, readings tend to be less precise as the sensor settles in. In one real-world study of pediatric patients with type 1 diabetes, the G7’s error rate dropped below 10% by day four, while the G6 took until about day six to reach the same threshold. This is why you might notice slightly jumpier numbers right after inserting a new sensor.
Neither the G6 nor the G7 requires routine fingerstick calibrations. You can optionally calibrate the G7 if you feel the readings are off, but it’s not built into the system the way earlier CGM generations required.
Warm-Up Period Before Readings Start
When you insert a new sensor, the system needs a brief warm-up before it begins sending readings. For the G7, that warm-up is 30 minutes. The G6 takes a full 2 hours. During this window you won’t receive any glucose data, so if you’re swapping sensors, plan accordingly. Many users insert a new sensor slightly before the old one expires to minimize the gap.
How Long Each Sensor Lasts
The standard Dexcom G7 sensor is approved for up to 10 days of continuous wear, followed by a 12-hour grace period. That grace period lets you keep receiving readings while you get a replacement sensor ready, but it’s not meant as an extension of normal use. Dexcom also offers a G7 15 Day version, which lasts up to 15 days with the same 12-hour grace period at the end. The G6 sensor lasts 10 days.
Over a 10-day sensor session, you’ll accumulate thousands of individual glucose data points without doing anything beyond the initial insertion.
What Happens When You Lose Signal
If your phone moves out of Bluetooth range of the sensor, or if you leave your phone behind, the readings pause on your display. But the sensor keeps measuring. Once you reconnect, the G7 can backfill up to 24 hours of missed readings, filling in the gaps on your trend graph as if you’d never been out of range. The older G6 stores and backfills up to 3 hours of data.
This matters in practical situations: sleeping with your phone in another room, leaving it in a locker at the gym, or temporarily losing connection in a crowded area. As long as the gap is within the backfill window, you won’t lose that data permanently.
How This Compares to Fingerstick Testing
A typical fingerstick routine might involve testing 4 to 10 times a day, depending on your treatment plan. Dexcom’s 288 daily readings represent a fundamentally different level of information. Fingersticks show you isolated moments. A continuous stream every 5 minutes reveals patterns: post-meal spikes, overnight dips, the effect of exercise, and how quickly you return to your target range.
The trend arrows on the Dexcom display are a direct benefit of that 5-minute frequency. Because the system has recent data points to compare, it can show you not just your current number but whether glucose is rising, falling, or holding steady, and how quickly. That context often matters more than the number itself when you’re deciding whether to eat, take insulin, or go for a walk.