GMI to A1C Calculator
Look at your Continuous Glucose Monitor (CGM) app. Take your 14-day or 90-day average glucose and instantly convert it into an estimated A1C percentage.
Last updated: March 3, 2026
Checking Your CGM
To use this calculator, open your Dexcom Clarity, Freestyle LibreView, or similar app. Look for the "Average Glucose" metric over a timeframe of at least 14 days.
For best accuracy, use an average from at least 14 days of continuous sensor data.
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GMI vs Lab A1C
GMI (Glucose Management Indicator) estimates what your lab A1C would be based only on your CGM data. Because lab A1C is affected by red blood cell lifespan and other biological factors, your actual lab A1C may be slightly higher or lower than your GMI.
Why GMI Might Differ From Your Lab A1C
It is extremely common for your calculated GMI (based on sensor data) and your clinical Lab A1C (drawn from a vein) to be slightly different. Here is why:
GMI (Sensor Data)
GMI measures the glucose in your interstitial fluid (fatty tissue just under the skin). It calculates a straight mathematical average from thousands of sensor readings every few minutes.
- Exclusively measures actual glucose averages
- Gives a precise snapshot of short-term timeframes (e.g. 14 days)
Lab A1C (Blood Draw)
A1C tests measure the percentage of your red blood cells that have sugar molecules attached to them (glycation). It estimates an average from the lifespan of those cells.
- Skewed higher if you have slow red blood cell turnover
- Skewed lower by bleeding, anemia, or kidney disease
Frequently Asked Questions
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