GMI vs A1C: what's the difference
Updated September 14, 2026
GMI (glucose management indicator) and lab A1C are related but not the same number. GMI is calculated from your average CGM glucose over a recent period (often about 14 days). Lab A1C is a blood test that reflects average glucose over roughly the past 2 to 3 months. Glynce shows a GMI-style estimate from your CGM data so you can spot longer-term patterns between lab visits. It is an indicator, not a lab result.
GMI vs A1C at a glance
| GMI | Lab A1C | |
|---|---|---|
| What it is | Estimate from CGM mean glucose | Blood test of glycated hemoglobin |
| Typical window | Often about 14 days of CGM | Roughly 2 to 3 months |
| Where you see it | CGM reports and apps like Glynce | Lab or clinic |
| Same as the other? | Not always | Not always |
Example chart: mean glucose to GMI
GMI (%) is commonly computed with the published formula GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL) (Bergenstal et al., Diabetes Care 2018). The table below is an illustrative lookup from that formula, rounded. Your own GMI can still differ from a lab A1C. This table explains the published population formula; it is not a personal target and not a reason to change insulin or treatment on your own.
| Mean glucose (mmol/L) | Mean glucose (mg/dL) | GMI (%) |
|---|---|---|
| 5.6 | 100 | 5.7 |
| 6.3 | 114 | 6.0 |
| 6.9 | 125 | 6.3 |
| 7.8 | 140 | 6.7 |
| 8.5 | 154 | 7.0 |
| 9.3 | 167 | 7.3 |
| 10.0 | 180 | 7.6 |
| 11.1 | 200 | 8.1 |
For a live calculator and the underlying formula, see the Jaeb Center GMI page. Numbers round; they are education, not a personal target.
Is GMI equal to A1C?
No. Searches for "GMI to A1C conversion" assume a fixed one-to-one map. GMI was introduced partly to replace the older "estimated A1c" label because the two measures often disagree. Differences can come from red blood cell lifespan, how glucose binds to hemoglobin, a recent short-term change in glucose, sensor versus lab measurement windows, and other individual factors. A gap does not automatically mean either number is wrong.
How to read GMI in Glynce
- It moves with your average CGM glucose over the period shown.
- It needs enough readings across that period to be meaningful.
- Read it together with time in range and variability, not alone.
FAQ
What does GMI stand for?
Glucose management indicator.
Can I convert GMI to A1C with a simple formula?
There is no reliable personal conversion that makes GMI equal lab A1C. The chart above maps mean CGM glucose to GMI using the published population formula. Lab A1C still comes from a blood test.
Which number should I trust?
Use both in context with your care team. Lab A1C remains the established clinic reference for long-term monitoring with your clinic. GMI helps you see what recent CGM averages imply between visits. Glynce does not replace lab tests or clinical advice.
This page is for education, not medical advice. Glynce helps you see patterns in glucose, food, and activity. It does not calculate or recommend insulin doses. Glynce is not a medical device or clinical tool. For questions about your numbers, talk with your care team. Contact support@glynce.app.
Sources: Bergenstal RM et al. Glucose Management Indicator (GMI): A New Term for Estimating A1C From Continuous Glucose Monitoring. Diabetes Care. 2018. doi:10.2337/dc18-1581; Jaeb GMI calculator.