The Adult BMI Chart, Band by Band

By Longevity Lab · Published: August 23, 2026

Based on peer-reviewed research — full source list at the end of this article. This is educational information, not medical advice.

The adult BMI chart runs from severe thinness below 16.0 to obesity class III at 40.0 and above, with the healthy band at 18.5 to 24.9 in the middle. Every boundary is a line drawn across a continuous risk curve, chosen because risk starts to move measurably at that point, and each band describes an average across a population rather than a fact about anyone in it. Below is the whole chart, what the evidence attaches to each band, and where the chart stops being informative.

The full chart

The weight column is there to make the bands concrete, and it changes with height — at 1.60 m the obesity threshold is 76.8 kg, at 1.85 m it is 102.7 kg. Our BMI calculator prints the band boundaries in kilograms for your own height.

The thinness bands

Three bands sit below 18.5 because the risk gradient is steep down there. The mortality curve is J-shaped: it rises on the left as well as the right, and by BMI 16 it is rising fast.

Interpretation depends almost entirely on one question: has this been stable for years, or did it appear recently? A stable low BMI in a small-framed adult who eats well and has normal bone density is a different situation from a 6 kg loss over four months, which needs investigating before anything else. Unintentional loss of more than 5% of body weight in six months is a clinical red flag at any starting point.

The healthy band, and why it is so wide

18.5 to 24.9 spans about 15 kg at average height because the underlying risk curve is genuinely flat across that range. The 2016 pooled analysis of 239 cohort studies found the minimum somewhere between 20 and 25 with little to separate points inside it.

A wide flat band is a feature, not vagueness. It means that within this range, weight is not the variable worth optimizing — blood pressure, fitness, sleep, muscle mass and waist all move outcomes more than a two-unit shift inside the band does.

Overweight: the band that depends most on other numbers

25.0 to 29.9 is where the index is least informative on its own. It contains muscular people whose risk is not raised at all, sedentary people carrying substantial abdominal fat whose risk is raised considerably, and a large majority somewhere in between.

What separates them is fat distribution. Abdominal obesity — fat carried inside and around the abdomen rather than under the skin of the hips and thighs — is what turns this band into risk. In the Emerging Risk Factors Collaboration’s analysis of 220,000 adults, waist circumference and waist-to-hip ratio predicted cardiovascular events at least as well as BMI, and adding them to a model that already had BMI improved it.

Practically: in this band, take your waist before you take any decision. Above 94 cm in men or 80 cm in women, the band means something. Below those figures, with normal blood pressure and glucose, it usually does not.

The three obesity classes

Obesity is split at 30, 35 and 40 because the associated risks are not on a gentle slope. Class I is associated with clearly raised rates of type 2 diabetes, hypertension and dyslipidemia. Class II adds a steeper rise in obstructive sleep apnea, weight-bearing joint disease and heart failure. Class III is associated with the largest reductions in life expectancy seen in cohort data, and it is the band where surgical and pharmacological treatment thresholds sit.

The classes also decide access to care in most health systems: eligibility for Risk of developing diabetes follow-up pathways, for structured weight management, for GLP-1 medication and for bariatric surgery are all written in terms of these numbers, usually with a lower threshold if a weight-related condition is already present.

In 2025 the Lancet Commission on clinical obesity argued that this is exactly where BMI-only classification breaks down, and proposed separating clinical obesity — where excess adiposity is already causing organ dysfunction — from preclinical obesity, where it is a risk factor and nothing more. Two people at BMI 33 can be in either category, and only measurement beyond the index tells you which. Screening for Metabolic syndrome is the usual next step, and Metabolic syndrome — the hidden pandemic of the 21st century scores the five criteria together.

What the chart cannot show

It has no input for muscle, so it misclassifies trained bodies. It has no input for fat distribution, so it misses the normal-BMI adult with a large waist entirely. It is read against thresholds derived largely from European populations, so it understates risk in people of Asian descent. And it drifts with age: after 65 the lowest-mortality band sits several units higher than the chart suggests.

Use the chart as the first of three numbers, not the only one. The other two are waist-to-height ratio and, if those two disagree, an actual body-composition measurement.

Frequently asked questions

Sources

Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.