What it means
The Homeostatic Model Assessment of Insulin Resistance (Matthews 1985) estimates how hard the pancreas is working to hold glucose in range. The formula: fasting insulin (µIU/mL) × fasting glucose (mg/dL) ÷ 405, or insulin (µIU/mL) × glucose (mmol/L) ÷ 22.5. A healthy, lean adult scores around 0.5–1.0; above 2.0 is generally taken as insulin resistance; above 2.9 in some populations is the cut-off used in research.
It is a steady-state estimate — a snapshot of liver insulin sensitivity — rather than a dynamic test like a clamp or glucose tolerance test.
Why it matters for longevity
Insulin resistance precedes type 2 diabetes by ten to fifteen years and sits upstream of visceral fat, fatty liver, high ApoB, hypertension and several cancers. In that decade, HbA1c and fasting glucose can look fine. HOMA-IR is the number that moves first, and it moves within weeks of a change in body fat, training or sleep.
What the evidence says
HOMA-IR correlates reasonably (r ≈ 0.6–0.8) with the euglycaemic clamp, the research gold standard. In cohorts, the top quartile of HOMA-IR predicts incident diabetes, cardiovascular disease and all-cause mortality, independently of BMI. In the San Antonio Heart Study, HOMA-IR predicted diabetes even in people with normal fasting glucose.
Its limits: fasting insulin assays vary between labs by 20–30%, so a trend from one lab beats a single value; it reflects liver rather than muscle insulin sensitivity; and it is less reliable in people on insulin or with impaired beta-cell function.
How to measure or use it
- Fasting glucose plus fasting insulin from the same draw after a 10–12 hour fast; many labs will report the index, or calculate it yourself.
- Targets: under 1.0 ideal, under 1.5 good, 1.5–2.0 watch, above 2.0 act. Fasting insulin alone under 6 µIU/mL is the equivalent single-number target.
- Levers: body-fat loss (the largest), endurance work, resistance training for the glucose sink, sleep, and fewer refined carbohydrates; retest at 8–12 weeks.
Related
- Metabolic health — the full panel, with targets
- Baseline labs — why fasting insulin is on the list
- The fat-loss protocol — HOMA-IR as a tracking number
Frequently asked questions
What is a good HOMA-IR?
Under 1.0 is ideal; under 1.5 is good; above 2.0 generally indicates insulin resistance. Reference ranges vary with population and assay.
How do I calculate it?
Fasting insulin (µIU/mL) multiplied by fasting glucose (mg/dL), divided by 405. With glucose in mmol/L, divide by 22.5 instead.
Why is it better than HbA1c?
It is not better; it is earlier. It rises years before HbA1c, while insulin is still holding glucose in range. Use both.
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