Dexcom sensors last 10 or 15 days depending on the model, and the system will alert you when it’s time to swap. The Dexcom G7 is approved for up to 10 days of wear, while the newer G7 15 Day lasts up to 15 days. Both versions include a 12-hour grace period after the session officially ends, giving you a window to apply a new sensor without losing glucose data.
Wear Time by Model
The G7 sensor runs for 10 days, then gives you an extra 12 hours to replace it. The G7 15 Day, as the name suggests, extends that to 15 days with the same 12-hour grace period. If you’re still using the older G6, each sensor session also lasts 10 days, and the separate transmitter that clips into the sensor has a battery life of about 3 months. Starting three weeks before the transmitter dies, you’ll see countdown warnings in the app.
The G7 models combine the sensor and transmitter into a single disposable unit, so there’s no separate transmitter to track. When the sensor session ends, you remove and discard the entire piece.
Warm-Up Time for a New Sensor
After inserting a fresh sensor, you’ll need to wait for a warm-up period before readings begin. The G7 takes 30 minutes. The G7 15 Day takes about 1 hour. During this time the sensor is calibrating to your body’s interstitial fluid, and you won’t see glucose numbers on your phone or receiver. Planning your swap around a time when you’re less dependent on real-time readings (like right before a meal rather than during exercise) can help minimize the gap.
Accuracy Stays Consistent Throughout the Session
A reasonable concern is whether readings become less reliable as the sensor ages. Data from a clinical study published through the American Diabetes Association found no meaningful drop-off. On day 1, the G6 sensor matched fingerstick values within 20% about 92.2% of the time. On day 10, that number was 92.5%. The average error rate was 9.3% on day 1 and 9.0% on day 10. In other words, the sensor performs just as well at the end of its life as it does at the beginning, so there’s no reason to replace it early out of accuracy concerns alone.
Signs You Need to Replace a Sensor Early
Sometimes a sensor fails before its scheduled end. You might see persistent “No Readings” alerts, readings that consistently don’t match how you feel, or a “Sensor Error” notification that doesn’t resolve after a few hours. If the sensor stops communicating with your phone entirely or gives wildly inaccurate numbers compared to a fingerstick check, it’s time to pull it off and start a new one.
Dexcom will replace sensors that fail before the session is supposed to end. Contact their tech support as soon as the problem happens. They’ll review the case, and if the sensor didn’t meet its expected performance, they’ll ship a replacement at no cost. Even sensors removed early for non-defect reasons (like you accidentally knocked it off or needed to remove it for a medical procedure) may qualify for a courtesy replacement.
Where to Place Your Next Sensor
The G7 is approved for the back of the upper arm for anyone age 2 and older. Children between 2 and 6 can also use the upper buttocks. The G7 15 Day is currently approved only for the back of the upper arm in adults 18 and older.
When placing a new sensor, keep it at least 3 inches (8 centimeters) from any insulin pump infusion set or injection site. Rotating between your left and right arm every session gives each site time to recover and helps prevent skin irritation from repeated adhesive contact in the same spot. Avoid placing the new sensor directly on top of where the old one sat.
Removing the Old Sensor Without Irritating Your Skin
Dexcom’s adhesive is designed to hold firmly for the full session, which means removal can sometimes tug at your skin. Start by loosening one edge with your fingernail. Then peel slowly at a low angle, folding the adhesive back on itself rather than pulling it straight up. Use your other hand to press the skin down and away from the adhesive as you go.
If the adhesive resists or the removal feels uncomfortable, adhesive remover wipes work well. Products like Uni-Solve, Tac Away, or AllKare wipes are specifically made for medical adhesive. For a cheaper option, baby oil, coconut oil, or olive oil can loosen the bond just as effectively. Rub the oil or wipe under the edge of the adhesive and work your way across gradually. After the sensor is off, gently clean the area to remove any remaining residue before placing a new sensor elsewhere.