The HOMA-IR Formula Explained, With a Worked Example

The HOMA-IR Formula

The standard HOMA-IR equation is:

HOMA-IR = (Fasting Insulin [µIU/mL] × Fasting Glucose [mg/dL]) ÷ 405

Both inputs need to come from a blood draw taken after an 8–12 hour fast, ideally in the morning before eating or drinking anything other than water, since both insulin and glucose shift significantly after meals. Our fasting insulin explainer covers why the fasting state matters and what a typical fasting insulin panel looks like.

A note on units: the constant 405 assumes glucose is reported in mg/dL, the standard unit in the United States. Labs that report glucose in mmol/L (common in Europe, Canada, and Australia) use a different constant — the formula becomes (fasting insulin × fasting glucose in mmol/L) ÷ 22.5. Using the wrong constant for your lab's units is the single most common HOMA-IR calculation error, so always check which unit your glucose result is reported in before doing the math by hand.

Worked Example: Calculating HOMA-IR Step by Step

Suppose a lab panel shows a fasting insulin of 12 µIU/mL and a fasting glucose of 95 mg/dL. Here is the calculation:

• Step 1: Multiply fasting insulin by fasting glucose: 12 × 95 = 1,140.
• Step 2: Divide by 405: 1,140 ÷ 405 ≈ 2.8.

A HOMA-IR of about 2.8 sits in a borderline-to-mildly-elevated range for many adults (see thresholds below), meaning this hypothetical result would generally prompt a closer look at diet, activity, and other metabolic markers rather than signal an emergency. Compare that to a second example: fasting insulin of 4 µIU/mL and fasting glucose of 85 mg/dL gives (4 × 85) ÷ 405 ≈ 0.8 — comfortably within the range most labs and researchers consider optimal insulin sensitivity.

Working through the numbers this way makes it clear why HOMA-IR moves the way it does: because insulin is multiplied by glucose rather than added to it, a rising fasting insulin level pushes the score up meaningfully even while glucose is still "normal" — which is exactly why HOMA-IR can flag insulin resistance years before fasting glucose alone would.

How to Interpret Your HOMA-IR Score

There is no single universally-adopted cutoff for HOMA-IR — thresholds vary somewhat by population, lab, and the research study cited — but the ranges below reflect commonly used, general benchmarks for non-pregnant adults:

These bands are general guidance, not diagnostic cutoffs — a physician interprets HOMA-IR alongside the rest of a metabolic panel, body composition, family history, and symptoms rather than as a standalone verdict. For the fuller clinical picture, including which other labs are typically checked alongside HOMA-IR, see insulin resistance testing and the insulin resistance overview.

HOMA-IR vs the TG/HDL Ratio: Two Different Math Approaches

HOMA-IR is not the only formula used to estimate insulin resistance from routine labs. The triglyceride-to-HDL ratio (TG/HDL) is a simpler alternative that some clinicians use, especially when fasting insulin was not drawn: divide a standard lipid panel's triglyceride value by the HDL cholesterol value, both in mg/dL. A ratio above roughly 3.0 is commonly cited as suggestive of insulin resistance, though — like HOMA-IR — this cutoff varies across sources.

The two formulas are not interchangeable. HOMA-IR uses direct measurements of insulin and glucose and is generally considered the more direct proxy for insulin action, while TG/HDL is a downstream marker: it reflects a lipid pattern (high triglycerides, low HDL) that frequently accompanies insulin resistance but does not measure insulin directly. TG/HDL is useful because a standard lipid panel is drawn far more often than fasting insulin, but when both values are available, HOMA-IR is generally preferred as the closer estimate.

Limitations of the HOMA-IR Formula

HOMA-IR is a validated and widely used research and clinical tool, but it has real limitations worth understanding before treating a single number as definitive. It assumes a simplified model of insulin-glucose feedback and was originally validated against the euglycemic clamp in specific study populations, so its accuracy can vary somewhat across different ages, body compositions, and health conditions. Insulin assays also differ between labs and manufacturers, meaning a fasting insulin value — and therefore the resulting HOMA-IR — is not always perfectly comparable across different laboratories. Results can also swing with recent illness, poor sleep, stress, or an insufficiently fasted sample.

Because of this, HOMA-IR is best used as one data point tracked over time with the same lab, alongside symptoms, waist circumference, and other markers such as A1C and fasting glucose — not as a single number that alone confirms or rules out insulin resistance.