Most continuous glucose monitors (CGMs) last between 7 and 15 days per sensor, depending on the brand and model. The one exception is an implantable option that lasts up to 6 months. Here’s a breakdown of every major CGM system currently available, what affects real-world sensor life, and how to get the most out of each session.
Sensor Lifespan by Brand and Model
Each CGM manufacturer has its own FDA-approved wear time. These are the current options:
- Dexcom G6: 10 days per sensor
- Dexcom G7: 10 days, plus a 12-hour grace period after the session officially ends
- Dexcom G7 15 Day: 15 days, plus a 12-hour grace period
- FreeStyle Libre 2: 14 days
- FreeStyle Libre 3: 14 days
- FreeStyle Libre 2 Plus: 15 days
- FreeStyle Libre 3 Plus: 15 days
- Medtronic Guardian 4: 7 days
- Eversense E3: 180 days (6 months), implanted under the skin by a healthcare provider
Once a disposable sensor reaches its expiration, it stops reporting glucose readings and you need to apply a new one. The Eversense E3 is different: it’s a small sensor placed under the skin of your upper arm in a quick office procedure, and it stays there for up to six months before needing replacement.
The Grace Period on Dexcom G7
Both versions of the Dexcom G7 give you a 12-hour grace period after the sensor session ends. During this window, you can still get readings while you prepare to swap in a new sensor. This is helpful if your session expires in the middle of the night or at an inconvenient time. Once those 12 hours are up, the sensor shuts off completely.
Warm-Up Time Before Readings Start
When you first apply a new sensor, it needs time to calibrate before it starts showing glucose data. This warm-up period varies:
- Dexcom G7: 30 minutes
- FreeStyle Libre 3: 1 hour
During warm-up, the sensor is adjusting to your body’s interstitial fluid (the fluid between your cells where CGMs actually measure glucose). You won’t receive any readings or alerts until warm-up is complete, so plan your sensor change accordingly, especially if you rely on low glucose alarms overnight.
Do Sensors Get Less Accurate Over Time?
A common concern is whether readings become unreliable toward the end of a sensor’s life. For most modern sensors, the answer is no. A study of a factory-calibrated CGM in children and adults found that accuracy on Day 1 and Day 10 was virtually identical, with error rates of 9.3% and 9.0% respectively. That’s a negligible difference, meaning you can generally trust the readings on the last day just as much as the first.
That said, individual sensors can degrade early due to physical factors like the sensor filament shifting under the skin, compression from sleeping on the sensor site, or excessive movement at the insertion area. If your readings suddenly seem off or you’re getting frequent error messages, the sensor itself may have failed rather than simply lost accuracy over time.
Early Sensor Failures
Not every sensor makes it to its full expiration date. An analysis of 2022 adverse event reports submitted to the FDA found that 6.2% of Dexcom G6 malfunction reports involved early sensor expiration. For the FreeStyle Libre, the most common reported issue was sensor errors requiring replacement, which accounted for 63.4% of injury-related reports. These numbers reflect reports to the FDA’s adverse event database, not overall failure rates across all users, but they do confirm that early failures happen with every brand.
If your sensor fails before its scheduled end date, most manufacturers will send a free replacement. Dexcom, Abbott, and Medtronic all have processes for reporting failed sensors through their apps or customer service lines.
Transmitter Battery Life (Dexcom G6)
If you use the Dexcom G6, the sensor and transmitter are separate components. While you replace the sensor every 10 days, the transmitter battery lasts about 3 months. Starting three weeks before the battery dies, you’ll get countdown warnings. Once it drops below 10 days of battery life, you won’t be able to start a new sensor session and the app will prompt you to pair a new transmitter.
Newer systems like the Dexcom G7 and FreeStyle Libre 3 have the transmitter built into the disposable sensor, so there’s no separate battery to track. You simply apply a new all-in-one unit each time.
Keeping Your Sensor On for the Full Duration
The most common reason people lose a sensor early isn’t a technical failure. It’s the adhesive peeling off. Swimming, sweating, showering, and just the friction of daily movement can loosen the patch that holds the sensor to your skin. A few strategies can help.
Before applying your sensor, make sure the skin is clean and dry, with no lotion or oils. Some people use a liquid skin adhesive product around the insertion area, let it dry, then place the sensor on the clean skin in the center. Products range from mild barrier wipes to stronger medical-grade adhesives for people who’ve had trouble with weaker options.
If the edges start lifting mid-session, adhesive overlay patches can extend the life of your sensor. Transparent film options like Tegaderm or IV3000 work well and are thin enough to be barely noticeable. For people who sweat heavily or are very active, a thicker fabric-style adhesive tape like Hypafix provides stronger hold, even when wet. When using overlay patches, cut a hole over the transmitter area so it isn’t covered.
How Many Sensors You’ll Need Per Month
Your monthly sensor count depends entirely on the model you use. With a 7-day sensor like the Guardian 4, you’ll go through about 4 sensors per month. A 10-day sensor like the Dexcom G7 means roughly 3 sensors per month. The 14- to 15-day options from Abbott and the Dexcom G7 15 Day bring that down to about 2 sensors per month. And the Eversense E3 requires just 2 sensor replacements per year.
This matters for both cost and convenience. Fewer sensor changes mean fewer supply shipments, less adhesive irritation from repeated applications, and less time spent on warm-up periods without glucose data. If minimizing sensor swaps is a priority, the longer-wear options are worth discussing with your care team.