CGM to A1C Calculator
Average Glucose to A1C Conversion Table
Based on the ADAG study formula. Time-in-range (TIR) estimates assume standard glucose variability.
| Avg Glucose (mg/dL) | Est. A1C (%) | Category | Approx. TIR (70-180) | Risk Level |
|---|---|---|---|---|
| 90 | 4.8% | Normal | >95% | Low |
| 110 | 5.5% | Normal | >90% | Low |
| 126 | 6.0% | Prediabetes | ~85% | Moderate |
| 140 | 6.5% | Prediabetes/Diabetes | ~75% | Elevated |
| 170 | 7.5% | Diabetes | ~55% | High |
| 212 | 9.0% | Diabetes (uncontrolled) | ~30% | Very High |
How We Calculate This
This cgm to a1c calculator uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
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This calculator converts between CGM average glucose readings and estimated A1C (also called Glucose Management Indicator, or GMI) using the standard ADAG formula. It also provides context on time-in-range metrics.
The basic rule:
- A1C = (average glucose in mg/dL + 46.7) / 28.7 (ADAG study formula)
- Average glucose = (A1C × 28.7) − 46.7 (reverse formula)
- Normal: A1C below 5.7% (avg glucose below 117 mg/dL)
- Prediabetes: A1C 5.7-6.4% (avg glucose 117-137 mg/dL)
CGM-derived average glucose may differ from lab A1C because A1C reflects a 3-month weighted average of red blood cell glycation, while CGM captures a 14-30 day average. Certain conditions (anemia, hemoglobin variants) can affect A1C accuracy. Always discuss results with your healthcare provider.
When Would You Use This Calculator?
This cgm to a1c calculator is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
How does CGM average glucose relate to A1C?
The ADAG study established the formula: A1C = (average glucose + 46.7) / 28.7. An average glucose of 120 mg/dL corresponds to approximately an A1C of 5.8%. CGM-derived estimates are now called GMI (Glucose Management Indicator) and may differ slightly from lab A1C.
What is a good time in range?
For most people with diabetes, the target is >70% time in range (70-180 mg/dL). For those without diabetes, >90% is typical. Less than 4% should be below 70 mg/dL (hypoglycemia). Each 5% improvement in time-in-range corresponds to roughly a 0.5% reduction in A1C.
Why might my CGM average differ from my lab A1C?
Lab A1C measures glycated hemoglobin over 2-3 months and is affected by red blood cell lifespan. CGM measures interstitial glucose over 14-30 days. Conditions like iron deficiency anemia, hemoglobin variants, kidney disease, or recent blood transfusions can cause lab A1C to be higher or lower than expected from glucose readings.
What is a normal average glucose?
For non-diabetic adults, average glucose is typically 80-100 mg/dL (A1C 4.6-5.4%). The prediabetes range is 117-137 mg/dL (A1C 5.7-6.4%). Optimal metabolic health advocates suggest targeting an average under 100 mg/dL with minimal spikes above 140 mg/dL.
What is GMI (Glucose Management Indicator)?
GMI is the term used for the A1C estimate derived from CGM data. It replaced the older term eA1C (estimated A1C) to clarify that it is a CGM-based calculation, not a lab measurement. GMI and lab A1C may differ by 0.3-0.5% in either direction, which is normal.
How often should I check my A1C?
For people with diabetes: every 3 months if adjusting treatment, or every 6 months if stable. For prediabetes: every 6-12 months. CGM users can track GMI continuously but should still get a lab A1C 2-4 times per year to confirm. The lab test captures information CGM does not.