Key Takeaways
- Dexcom G7 is the best all-around CGM for accuracy, real-time alerts, and ease of use
- FreeStyle Libre 3 is the best value option if you don't need real-time alerts, with scan-based glucose readings every 15 minutes
- Medtronic Guardian is best for people using insulin pumps who want integrated pump-CGM system
- All CGMs require a prescription and insurance coverage varies; out-of-pocket cost is typically $40-100/month if not covered
- Accuracy differences between brands are minimal; the best CGM is the one you'll actually use consistently
Continuous glucose monitors (CGMs) have transformed diabetes management by providing real-time glucose data instead of just fingerstick checks a few times daily. If you're trying to understand your glucose patterns — whether you have type 1 diabetes, type 2 diabetes, or prediabetes — a CGM gives you the information you need to make better dietary and lifestyle decisions.
This article compares the three major CGM systems available in 2025, breaks down the differences, and helps you decide which is best for your situation. Combined with proper fasting glucose understanding, CGMs give you complete glucose control insights.
Overview: The Three Major CGM Systems
| Device | Real-Time Alerts | Wear Time | Avg Monthly Cost (Uninsured) | Best For |
|---|---|---|---|---|
| Dexcom G7 | Yes, smartphone app | 10.5 days | $60-75 | Real-time monitoring, type 1 diabetes |
| FreeStyle Libre 3 | Optional (FreeStyle app) | 14 days | $40-50 | Value-conscious, type 2 diabetes |
| Medtronic Guardian | Yes, integrated with pump | 7 days | $80-100 | Insulin pump users, closed-loop systems |
Dexcom G7: Best Overall CGM for 2025
Accuracy: Within 9.5% mean absolute relative difference (MARD) from lab reference glucose — excellent accuracy across high and low glucose ranges.
Key features:
- Real-time glucose readings every 5 minutes sent to your smartphone automatically
- Customizable high and low glucose alerts
- Wear time of 10.5 days per sensor (you typically wear 2 sensors per month)
- Wireless data sharing to family members or caregivers (useful for parents managing children with T1D)
- Integrates with most insulin pumps and diabetes apps (including MetabolicOS for manual logging)
- Small sensor (5mm probe depth) — minimal insertion pain
Cost: $60-75/month out of pocket (uninsured). Usually covered by insurance for type 1 diabetes patients; variable coverage for type 2 diabetics on insulin.
Pros: Most accurate in low glucose ranges (critical for safety). Real-time alerts prevent dangerous hypoglycemia. Best smartphone integration. Longest sensor life means fewer insertion site changes. Best for people who check glucose frequently throughout the day.
Cons: Highest cost of the three options. Requires smartphone to receive alerts (though optional readings are still available). Not ideal for people who rarely check their glucose.
FreeStyle Libre 3: Best Value Option
Accuracy: Within 9.2% MARD from reference glucose — very similar accuracy to Dexcom G7, slightly better in some glucose ranges.
Key features:
- Scan-based readings every 15 minutes (you hold your phone or reader over the sensor to check glucose)
- Optional real-time alerts if you enable FreeStyle app notifications
- Longest wear time of 14 days per sensor (roughly 2.5 sensors per month)
- Smallest and thinnest sensor of the three options (35mm, 5.3mm thick)
- No calibration required — straight out of the package
- Flash glucose monitoring means you control when to check
Cost: $40-50/month out of pocket (uninsured). Often covered by Medicare and many commercial plans, even for type 2 diabetes patients.
Pros: Lowest cost option. No fingerstick calibration needed. Longest wear time per sensor reduces insertion frequency. Good accuracy throughout normal glucose ranges. Works well for type 2 diabetes management where real-time alerts are less critical.
Cons: You must actively scan the sensor to see glucose (not automatic like Dexcom). 15-minute delay in readings. Fewer third-party app integrations. Real-time alerts are an add-on, not standard. Requires NFC-capable smartphone.
Medtronic Guardian 4: Best for Pump Lovers
Accuracy: Within 12-15% MARD — slightly lower accuracy than Dexcom and Libre, but still excellent for clinical use.
Key features:
- Direct integration with Medtronic insulin pumps (Minimed 780G and newer)
- Real-time glucose readings automatically sent to insulin pump display
- Works with Medtronic's hybrid closed-loop insulin delivery (automatic insulin adjustments based on glucose)
- Wear time of 7 days per sensor (requires frequent sensor changes)
- Bluetooth connectivity to dedicated receiver or smartphone
- Integrated low glucose suspend function with compatible pumps
Cost: $80-100/month out of pocket (typically well-covered by insurance due to pump integration). Often bundled with insulin pump replacement costs.
Pros: Seamless integration with insulin pumps eliminates need for separate glucose display. Hybrid closed-loop automatically adjusts insulin based on glucose trends. Best option if you're already invested in Medtronic pump ecosystem. Real-time alerts built in.
Cons: Highest cost overall. Shorter wear time (7 days) means more frequent sensor changes and higher replacement cost. Medtronic ecosystem only — limited third-party app integration. Slightly lower accuracy in low glucose ranges compared to Dexcom.
Important: All three CGMs require an FDA prescription. Your healthcare provider must write a prescription for the CGM, and insurance approval is required in most cases. Ask your doctor specifically about which CGM your insurance covers.
Comparing CGM Accuracy in Real-World Use
Clinical trials show all three devices are highly accurate. However, real-world accuracy depends on:
- Insertion site: Abdomen is most accurate for all three. Arm is acceptable but slightly less accurate.
- Hydration: Dehydration reduces sensor accuracy.
- Sweat and water exposure: Chlorine and salt water can damage sensors and reduce accuracy.
- Calibration (if required): For devices requiring fingerstick calibration, accuracy depends on accurate calibration fingersticks.
- Sensor age: Some devices show slight accuracy drift in the last 1-2 days of wear.
In clinical practice, differences in accuracy between brands are small enough that they don't significantly affect management decisions. More important is choosing a system you'll actually use consistently.
Insurance Coverage and Cost in 2025
Type 1 Diabetes: Most commercial insurance plans and Medicare now cover CGMs. Dexcom and FreeStyle Libre are usually covered at least partially. Out-of-pocket costs typically $0-50/month after deductible/copay.
Type 2 Diabetes on Insulin: Variable coverage. Many plans cover Dexcom G7 and FreeStyle Libre 3 if you're on insulin. Some plans require prior authorization or a trial of less expensive CGMs first.
Type 2 Diabetes not on Insulin (Prediabetes): Usually not covered by insurance. Out-of-pocket cost is full price ($40-100/month depending on device).
Cost-saving strategies:
- Ask your doctor if your insurance covers CGMs; some primary care docs don't know their plan's coverage
- If not covered, FreeStyle Libre 3 offers the best value at $40-50/month
- Some states have Medicaid programs covering CGMs for type 2 diabetes; check your state's coverage
- Manufacturer patient assistance programs may be available if cost is a barrier
Which CGM Should You Choose?
Choose Dexcom G7 if:
- You have type 1 diabetes or are on intensive insulin therapy
- You need real-time alerts for safety and glucose optimization
- You check your glucose frequently and want the most data points
- Your insurance covers it and cost is not a major concern
Choose FreeStyle Libre 3 if:
- You have type 2 diabetes and want to optimize glucose trends
- Cost is a primary concern and you don't need constant real-time alerts
- You prefer control over when you check glucose (scanning vs. automatic readings)
- Your insurance covers it (common for Libre)
Choose Medtronic Guardian if:
- You use a Medtronic insulin pump (780G or newer)
- You want fully integrated closed-loop insulin delivery
- Your insurance covers it as part of pump therapy
Frequently Asked Questions
Do I need a prescription for a continuous glucose monitor?
Yes, all FDA-approved CGMs require a prescription. Your doctor must write a prescription for Dexcom, FreeStyle Libre, or Medtronic Guardian. However, some CGM companies offer telemedicine visits if your primary care physician won't write the prescription.
Is continuous glucose monitoring covered by insurance?
Coverage varies significantly by insurance plan and whether you have type 1 or type 2 diabetes. Most plans cover Dexcom and FreeStyle Libre for type 1 diabetes and some type 2 patients on insulin. Out-of-pocket costs (if not covered) range from $40-100 per month. Ask your insurance specifically about coverage before purchasing.
Which CGM has the best accuracy?
All FDA-approved CGMs are highly accurate (within 10-20% of actual blood glucose). Dexcom G7 and FreeStyle Libre 3 have similar accuracy overall, with Dexcom G7 slightly more accurate in low glucose ranges. Real-world accuracy depends more on proper sensor placement and calibration than device brand.
Can I use a CGM if I don't have diabetes?
You need a prescription, which typically requires a diabetes or prediabetes diagnosis. However, some companies offer limited telemedicine options for non-diabetics interested in glucose optimization. Check with your healthcare provider about options for metabolic health tracking outside of diabetes diagnosis.