HOMA-IR calculator (and QUICKI from the same two values)

What HOMA-IR is

HOMA stands for homeostatic model assessment. It was published by Matthews and colleagues in Diabetologia in 1985 as a way to estimate two things — insulin resistance and beta-cell function — from a single fasting blood sample, at a time when the alternative was a hyperinsulinaemic-euglycaemic clamp that takes hours and a hospital.

The logic is simple. In a healthy system, a certain amount of insulin holds fasting glucose at a certain level. If your glucose is normal but your insulin is high, your body is paying more than it should to keep it there. HOMA-IR is the product of the two, scaled by a constant so that a healthy young adult scores about 1.

This is what people usually mean when they search for an insulin resistance calculator. It is also why the fasting insulin value matters: a fasting glucose alone cannot tell the difference between a body that is coping easily and one that is compensating hard.

The formula, in both unit systems

With glucose in mg/dL, HOMA-IR is fasting insulin in µIU/mL multiplied by fasting glucose, divided by 405. With glucose in mmol/L the same relationship uses 22.5 instead, because 405 divided by 18.0156 — the mg/dL per mmol/L of glucose — is 22.5. The calculator accepts either and converts internally, so the two routes give the same answer.

QUICKI, the quantitative insulin sensitivity check index, is computed from exactly the same pair of values: one divided by the sum of the base-ten logarithms of insulin and of glucose in mg/dL. It was published by Katz and colleagues in 2000 and behaves better than HOMA-IR at the sensitive end of the range, which is why it is shown alongside. Higher QUICKI means more sensitive; higher HOMA-IR means less.

Insulin must be a fasting value in µIU/mL, which most laboratories also write as mIU/L — the two units are numerically identical. If your report gives insulin in pmol/L, convert it before entering it. The factor is roughly six, but its exact value depends on the standard your laboratory's assay is traceable to, so take it from the laboratory rather than from a website. Entering pmol/L unconverted overstates HOMA-IR several times over.

The bands, and why they are not a diagnosis

There is no internationally agreed cut-off for HOMA-IR. No professional body defines a threshold the way the American Diabetes Association defines one for HbA1c. What exists is a set of population studies, each reporting the upper limit of normal in the group it studied, and those limits differ by ethnicity, age, body composition and — critically — by which insulin assay the laboratory used. Insulin assays are not standardised between manufacturers the way glucose assays are.

The two boundaries on this page are named published values rather than a house opinion: the lower one is the figure that best separated people with and without metabolic syndrome in a large Spanish population study, and the upper one is the lower limit of the top quintile in the Bruneck study, an Italian population cohort. Both are printed with their citation under the scale, along with the span the other published cut-offs cover — which is wide. They are an orientation, nothing more. If your laboratory printed its own reference range next to your insulin result, that range wins.

The authors of the original paper were blunt about precision too: they reported coefficients of variation around 30 % for the estimate and wrote in the abstract that this limits its use. A small move between two tests is noise, not a trend.

Because of the assay problem, a HOMA-IR from one laboratory should not be compared with one from another. Tracking your own value at the same laboratory over time is far more informative than comparing your number with a stranger's.

When HOMA-IR does not apply

The model assumes your pancreas is still producing insulin and responding to glucose. It is therefore not valid in type 1 diabetes, in advanced type 2 diabetes with substantial beta-cell failure, or in anyone taking insulin — the measured insulin is then partly the injected kind, and the arithmetic is meaningless.

It also needs a genuine fasting sample, normally eight to twelve hours without food. A sample taken two hours after breakfast will give a number, and the number will be wrong. Acute illness, recent heavy exercise and pregnancy all move it too.

If fasting insulin is simply not available to you — many general practices will not order it — the TyG index estimates the same thing from triglycerides and glucose, both of which are on a standard lipid panel.

What to do with a raised result

A raised HOMA-IR is a starting point for a conversation, not an outcome. The first thing worth knowing is whether it is consistent, which means repeating the test rather than acting on one reading.

The dietary lever with the most direct connection to fasting insulin is the amount of carbohydrate arriving at once, which is what the glycemic load calculator measures. Muscle matters too, because skeletal muscle is where most glucose is disposed of — there is a piece on that. And if you want the plain-language version of what insulin resistance feels like from the inside, read the self-check.