The Truth About CGM Delay: What 15 Minutes Really Means
Continuous Glucose Monitors (CGMs) have completely changed the way people with diabetes track blood sugars. These small devices give you automatic readings every few minutes-no more constant finger pricks, no guessing, just data.
But there’s one important thing many people don’t realize: CGMs have a natural 10–15 minute delay between what your device shows and what’s actually happening in your bloodstream.
Why CGMs Have a Delay
CGMs measure glucose in your interstitial fluid (the fluid around your cells), not directly from your blood. Because glucose takes time to move from the bloodstream into that fluid, your CGM readings will always lag slightly behind your real-time blood sugar levels.
Most of the time, this delay doesn’t cause major issues-but it matters during fast changes, like after eating, exercising, or dosing insulin.
The Problem with Overcorrecting
Let’s say your CGM shows a blood sugar of 264 and trending up. You take insulin to bring it down, but your real-time blood sugar might already be leveling off-or even starting to drop.
This is how overcorrecting happens. Acting too quickly can cause a low later, starting a frustrating cycle of highs and crashes.
How to Handle the CGM Delay
To make the most of your CGM:
- Watch trends, not single numbers. Notice the direction and speed of change.
- Double-check before correcting. When unsure, do a quick fingerstick test.
- Be patient after insulin. It can take time for your CGM to “catch up.”
- Work with your care team. Your dietitian or diabetes educator can help you interpret your data correctly.
The Bottom Line
CGMs are powerful tools for managing diabetes, but they’re not perfect. Understanding the 15-minute delay helps you use the data more effectively and avoid unnecessary corrections.
Think of your CGM as a guide-not an exact measurement-and always pair it with awareness and support from your healthcare team. That’s how you’ll get the most accurate insights and smoother blood sugars.
