Continuous glucose monitors report a glucose management indicator (GMI), which estimates the A1c you would expect from your sensor data. It is useful between lab tests but can differ from a lab A1c by 0.5% or more.
How to use the Hemoglobin A1c Calculator
- Average glucose
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter your average glucose over at least 2 weeks of sensor data (or many meter readings). The calculator applies both the ADAG and GMI equations.
Diagnostic thresholds (ADA)
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| HbA1c | below 5.7% (39 mmol/mol) | 5.7–6.4% (39–47) | 6.5% (48) or higher |
| Fasting glucose | below 100 mg/dL (5.6 mmol/L) | 100–125 mg/dL (5.6–6.9) | 126 mg/dL (7.0) or higher |
| 2-hour OGTT | below 140 mg/dL (7.8 mmol/L) | 140–199 mg/dL (7.8–11.0) | 200 mg/dL (11.1) or higher |
| Random glucose with symptoms | 200 mg/dL (11.1) or higher |
What each result means
- Estimated A1c (ADAG) = ([Average glucose] + 46.7)÷28.7
- Glucose management indicator (GMI) = 3.31 + 0.02392×[Average glucose]
- Estimated A1c in IFCC units = ([Estimated A1c (ADAG)] – 2.15)×10.929
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
A1c (%) = (average glucose mg/dL + 46.7) ÷ 28.7
IFCC (mmol/mol) = (A1c % − 2.15) × 10.929
Glucose management indicator (GMI, CGM) = 3.31 + 0.02392 × mean glucose (mg/dL)
Worked example
Inputs — Average glucose: 154 mg/dL.
Results — Estimated A1c (ADAG) = 7 %; Glucose management indicator (GMI) = 7 %; Estimated A1c in IFCC units = 53 mmol/mol; Category (ADA) = Diabetes range.
Key terms
- GMI
- Glucose management indicator.
- NGSP
- National Glycohemoglobin Standardization Program (% units).
Frequently asked questions
Is GMI the same as A1c?
No – GMI is estimated from sensor glucose, while A1c is measured in blood. They usually agree within about 0.5%.
How many days of CGM data do I need?
At least 14 days with 70% sensor wear.
Can A1c be used to diagnose diabetes in everyone?
Not in some conditions, such as pregnancy, recent blood loss or haemoglobin variants.