GMI Calculator (Glucose Management Indicator)
Turn your CGM average glucose into your glucose management indicator (GMI) — the modern, CGM-based estimate of your A1c-equivalent, in both % and mmol/mol.
Your mean sensor glucose, ideally over 14+ days.
How to Use This Calculator
- Choose your glucose units — mg/dL or mmol/L.
- Enter your CGM average (mean) glucose, ideally from at least 14 days of data with good sensor wear.
- Read your GMI in both % and mmol/mol.
GMI estimates your A1c from CGM data; it can differ from a lab A1c by 0.3% or more, so use it alongside — not instead of — your clinician's testing.
How GMI Is Calculated
The glucose management indicator replaced the older "estimated A1c" label. It is calculated directly from your mean CGM glucose using a validated regression equation, giving a number on the same scale as A1c:
Example: a mean glucose of 154 mg/dL → 3.31 + 0.02392 × 154 = GMI ≈ 7.0%.
GMI by Average Glucose
| Mean glucose (mg/dL) | GMI (%) |
|---|---|
| 126 | 6.3 |
| 154 | 7.0 |
| 183 | 7.7 |
| 212 | 8.4 |
| 240 | 9.1 |
Use at least 14 days of CGM data (ideally with >70% sensor wear) for a reliable GMI.
GMI on Your CGM Report (AGP) & Target Goals
The standardized AGP report
GMI appears at the top of the Ambulatory Glucose Profile (AGP) — the one-page summary your CGM software produces (Dexcom Clarity, LibreView, Tidepool). Alongside GMI it shows your average glucose, time in range, and glucose variability, giving a fuller picture than a single number.
Recommended CGM targets
International consensus targets for most adults with type 1 or type 2 diabetes are:
| Metric | Goal |
|---|---|
| Time in range (70–180 mg/dL) | > 70% |
| Time below range (< 70 mg/dL) | < 4% (< 1% below 54) |
| Time above range (> 180 mg/dL) | < 25% |
| GMI | < 7% |
| Glucose variability (CV) | ≤ 36% |
Targets are looser for older or higher-risk people and tighter in pregnancy. Your care team sets your individual goals.
GMI Lookup Table: Mean Glucose → GMI
Computed from the published formula GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL) (Bergenstal et al., Diabetes Care 2018).
| Mean glucose (mg/dL) | Mean glucose (mmol/L) | GMI (%) | GMI (mmol/mol) |
|---|---|---|---|
| 100 | 5.6 | 5.7 | 39 |
| 114 | 6.3 | 6.0 | 42 |
| 125 | 6.9 | 6.3 | 45 |
| 140 | 7.8 | 6.7 | 50 |
| 154 | 8.6 | 7.0 | 53 |
| 167 | 9.3 | 7.3 | 56 |
| 180 | 10.0 | 7.6 | 60 |
| 200 | 11.1 | 8.1 | 65 |
| 220 | 12.2 | 8.6 | 70 |
| 240 | 13.3 | 9.1 | 76 |
| 260 | 14.4 | 9.5 | 80 |
| 280 | 15.5 | 10.0 | 86 |
| 300 | 16.7 | 10.5 | 91 |
The often-quoted anchor: a 14-day mean of 154 mg/dL ≈ GMI 7.0%. For the reverse direction (A1c → average glucose), use the HbA1c / eAG calculator.
When GMI and Lab A1c Disagree
In the original Bergenstal dataset, only about half of people had a GMI within 0.3% of their lab A1c — disagreement is normal, not an error. Persistent gaps come from real physiology:
- Red-cell lifespan: longer-lived red cells accumulate more glycation → lab A1c reads higher than GMI; shorter lifespan (anemia, hemolysis, kidney disease, recent blood loss) → A1c reads lower.
- Glycation rate variability: individuals glycate hemoglobin at different rates at the same glucose level.
- Hemoglobin variants & pregnancy can distort the A1c assay itself.
- Sensor bias or poor wear time (<70% over 14 days) can distort the GMI side instead.
Clinically, a stable personal gap is useful information: if your GMI always runs ~0.4% below your lab A1c, your team can calibrate targets around your pattern. A gap that suddenly changes is worth investigating (new anemia, kidney change, sensor issue).
Frequently Asked Questions
What is GMI and how is it different from A1c?
GMI (glucose management indicator) estimates your A1c from CGM average glucose over a set period. A1c is a blood test reflecting roughly 2–3 months of glucose. GMI and A1c often differ slightly because they measure in different ways.
Why is my GMI different from my lab A1c?
Individual biology — red blood cell lifespan and how glucose attaches to hemoglobin — varies. So two people with the same GMI can have different lab A1c values. A persistent gap is worth discussing with your clinician.
How much CGM data do I need for an accurate GMI?
At least 14 days of CGM data with good sensor wear (over about 70% of the time) gives a representative GMI. Shorter or patchy data can skew the average glucose and the resulting GMI.
Is GMI the same as estimated average glucose (eAG)?
No. GMI converts average glucose into an A1c-like percentage. eAG goes the other way — it converts an A1c into an average glucose. See our eAG ↔ A1c calculator for that conversion.
What is a good GMI?
For most adults with diabetes, a GMI under 7% is the common target, mirroring the usual A1c goal. Goals are individualized — looser for older or higher-risk people and tighter in pregnancy — so confirm your personal target with your care team and read GMI alongside your time in range.
Where do I find my GMI?
Your CGM software calculates it automatically and shows it on the Ambulatory Glucose Profile (AGP) report — in apps such as Dexcom Clarity, LibreView or Tidepool. If you only have your average glucose, this calculator gives you the same number.
Sources
- Bergenstal RM, et al. Glucose Management Indicator (GMI): A new term for estimating A1C from CGM. Diabetes Care. 2018.
- American Diabetes Association. Standards of Care — CGM metrics and time in range.
Last reviewed: July 2026