The Dexcom G7 checks your glucose levels once every 5 minutes. That adds up to more than 280 readings per day, giving you a near-continuous picture of where your glucose is heading, not just where it was at a single point in time.
What the Sensor Actually Measures
The G7 doesn’t measure blood sugar directly. Instead, a tiny filament sits just under your skin and measures glucose in the fluid between your cells, called interstitial fluid. Glucose moves from your bloodstream into this fluid naturally, so the two track closely, but not identically.
Research published by the American Diabetes Association found the G7 has an average lag time of about 2 minutes between what’s happening in your blood and what the sensor reports. That’s fast enough that you rarely notice a difference in everyday use. Interestingly, about a third of sensors in the study actually detected glucose changes slightly ahead of blood values, likely due to the G7’s onboard algorithm predicting where glucose is heading based on the trend.
How Readings Reach Your Phone or Receiver
Every 5 minutes, the sensor transmits its latest reading over Bluetooth to your smartphone, smartwatch, or standalone receiver. Dexcom rates the Bluetooth range at up to 33 feet, though the system needs you within about 20 feet for continuous, reliable data flow. If you walk out of range temporarily, the sensor stores readings and backfills them once you’re close enough again, so short gaps in connectivity don’t mean lost data.
Warm-Up and Sensor Lifespan
When you first apply a G7 sensor, there’s a warm-up period before readings begin. The standard 10-day sensor takes about 30 minutes to warm up. The newer 15-day version requires 60 minutes because it uses a different algorithm to support the longer wear time.
Once warm-up finishes, the 10-day sensor runs continuously for its full session plus a 12-hour grace period at the end. During that grace period you still receive readings, giving you time to apply a new sensor without a gap in data. The sensor cannot be restarted after the session ends.
How Accurate Are Those 5-Minute Readings?
Accuracy in continuous glucose monitors is typically measured by something called MARD, which is the average percentage difference between the sensor reading and a lab reference value. Lower is better. In a head-to-head clinical study of 55 adults, the G7 showed a MARD of 13.6%, with about 78.6% of readings falling within 20 mg/dL (or 20%) of the reference value. For context, that’s accurate enough for the FDA to approve the G7 for making treatment decisions without confirming with a fingerstick in most situations.
Accuracy can vary within a sensor session. The same study found that the G7 performed best during the first 12 hours after insertion, then showed slightly wider variation in the following 12 hours. Day-to-day, most users find the readings reliable enough to dose insulin from, but Dexcom still recommends using a traditional blood glucose meter if your symptoms don’t match what the sensor is showing.
No Fingerstick Calibration Required
Unlike older continuous monitors, the G7 is factory calibrated. You don’t need to enter fingerstick values to keep it accurate. The sensor arrives pre-calibrated and maintains that calibration throughout its entire wear period. The only time you’d reach for a fingerstick meter is when your reading and your symptoms disagree, for example, if the sensor shows a normal number but you feel shaky and sweaty.
What Happens Between Readings
Five-minute intervals are frequent enough to power some genuinely useful features. The G7 uses the pattern of recent readings to project where your glucose is heading and can warn you up to 20 minutes before a predicted severe low (below 55 mg/dL). This “Urgent Low Soon” alert is especially valuable overnight, when you’re asleep and can’t feel symptoms.
The system also calculates your “time in range,” the percentage of the day your glucose stays within your target zone, typically 70 to 180 mg/dL. With 280-plus data points per day, this metric gives a far more complete picture than the handful of snapshots you’d get from fingersticks alone. Many endocrinologists now consider time in range just as important as A1C for understanding overall glucose management.