Lower BMI thresholds and what they change
A 2004 WHO expert consultation found that Asian populations carry a higher proportion of body fat and face raised risk of type 2 diabetes and cardiovascular disease at BMI values below 25. It kept the international classification unchanged and instead named 23.0, 27.5, 32.5 and 37.5 as points for public health action, leaving each country to decide which apply. At 170 cm and 68 kg the BMI is 23.5: healthy weight on the international bands, increased risk on the lowered ones.
Adult bands at this height
| Underweight | 0 | Under 18.5 | 53.4 and under | 117.8 and under |
| Increasing but acceptable risk | 18.5 | 18.5 to under 23.0 | 53.5 – 66.4 | 117.9 – 146.5 |
| Increased risk | 23 | 23.0 to under 27.5 | 66.5 – 79.4 | 146.6 – 175.2 |
| High risk | 27.5 | 27.5 and over | 79.5 and over | 175.3 and over |
An estimate, not medical advice. Body metrics are population averages and do not account for your individual circumstances. Speak to a clinician about anything that matters.
23.5 at 170 cm sits in two different bands depending on which cut-offs are used, and neither reading is a diagnosis of anything.
WHO did not replace the international classification. It added action points, which is a different kind of statement: a trigger for intervention rather than a category.
On the lowered points the acceptable band at 170 cm is 53.5 kg to 66.4 kg, against 53.5 kg to 72.2 kg on the international ones — a top end 5.8 kg lower.
How it works
The formula
BMI = weight / height^2
= kilograms / metres squared
Imperial input is converted first, and exactly:
1 in = 2.54 cm 1 lb = 0.45359237 kg
The band is decided on the unrounded BMI:
under 18.5 underweight
18.5 to under 25 healthy weight
25 to under 30 overweight
30 and over obesity
On the lowered action points the middle two
cut-offs move to 23 and 27.5.
A band's weight range is the same formula run
backwards:
weight = BMI x metres squared
and each end is rounded inwards to a tenth -
the bottom up, the top down - so every weight
printed is inside the band it is listed under.
What it assumes
- The band is decided on the unrounded BMI, not on the figure displayed. A BMI shown as 25.0 can still read as healthy weight, because the value before rounding was 24.97 and a cut-off is a number rather than a display.
- Below the age of 20 the adult bands are withheld. BMI at that age is read against a BMI-for-age reference, where the same figure means different things at 12 and at 17, so applying the adult bands to a child does not approximate the answer, it gives the wrong one.
- Each weight range is rounded inwards to a tenth, so every weight shown is genuinely inside its band. The consequence is a tenth of a kilogram between one band's top and the next band's bottom, and that gap is the boundary itself rather than a missing case.
- The kilogram and pound ranges are each rounded in their own unit rather than one being converted from the other, so the pound range is the tightest true pound range and is not always the exact conversion of the kilogram one.
- BMI carries no term for body composition, fat distribution or frame. Muscle is denser than the fat it replaces, so a trained athlete lands high on a body that is not overweight, and somebody who has lost muscle with age can land in the healthy band while carrying more fat than they used to.
- Pregnancy cannot be detected from a height and a weight, and the adult bands do not apply during it or while breastfeeding.
- The lowered cut-offs are points for public health action rather than a second classification. The 2004 WHO consultation kept the international bands unchanged and named 23.0 and 27.5 as triggers, leaving each country to decide where they apply.
Common questions
Where do the lower thresholds come from?
From WHO's 2004 review of Asian populations and NICE's 2013 guidance for the UK. Both found that the risk of type 2 diabetes and cardiovascular disease rises at a lower BMI in South Asian, Chinese, Black African and African-Caribbean groups, so the action points were moved down rather than the bands renamed.
Does a lower threshold make the healthy range smaller?
Yes. The lower bound stays at 18.5 while the upper action point moves from 25 to 23, so the band narrows rather than shifts. That is deliberate: it marks the point at which a clinician would start a conversation, not a claim that a lower weight is better.
Sources
- Obesity and overweight
- Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies
- Heart-Healthy Living: Aim for a Healthy Weight
- Growth reference data for 5-19 years — BMI-for-age
- NIST Guide to the SI (Special Publication 811), Appendix B: conversion factors
Method written and checked by Tessalor on Jul 30, 2026.
The full method, worked example and every assumption behind this figure are on BMI Calculator.