Turn your BMI into a simple ratio against the standard 25 kg/m² threshold, and find out exactly what weight corresponds to any BMI goal you choose. Both figures are direct mathematical extensions of the standard BMI formula.
BMI Prime is your regular BMI divided by 25, so it shows how far your BMI sits from the widely used "normal-to-overweight" boundary as a simple decimal — under 1.0 means your BMI is below 25, over 1.0 means it's above 25. Target weight simply rearranges the same BMI formula so that, instead of weight and height producing a BMI, your height and a chosen BMI produce a weight figure. Neither calculation introduces a new health metric — both are straightforward algebraic restatements of the same standard BMI equation already used on this site's BMI calculator.
| Category | BMI Range | BMI Prime Range | Your Status |
|---|
BMI Prime is a way of expressing your Body Mass Index as a proportion rather than a raw kg/m² figure. Because the number 25 kg/m² is already the standard upper edge of the WHO "healthy weight" range — the same threshold used on this site's main BMI calculator — dividing any BMI by 25 turns that boundary into a clean reference point of exactly 1.0. A BMI Prime below 1.0 places someone below the 25 line, a BMI Prime above 1.0 places them above it, and the size of the decimal shows, at a glance, roughly how far off that line they sit.
BMI Prime is calculated in two short steps: first the standard BMI formula, then a single division by 25.
Because BMI Prime is just BMI divided by a constant, every standard BMI category maps onto a matching BMI Prime range. The table below shows how the familiar WHO categories translate into BMI Prime figures.
| BMI Prime | Equivalent BMI | Category |
|---|---|---|
| Below 0.74 | Below 18.5 | Underweight |
| 0.74 – 1.00 | 18.5 – 24.9 | Healthy weight |
| 1.00 – 1.20 | 25.0 – 29.9 | Overweight |
| 1.20 – 1.40 | 30.0 – 34.9 | Obese Class I |
| 1.40 – 1.60 | 35.0 – 39.9 | Obese Class II |
| 1.60 and above | 40.0 and above | Obese Class III |
The target weight tool answers a different question: instead of "what is my BMI at my current weight?" it asks "what weight would give me a chosen BMI at my current height?" It does this by rearranging the standard BMI formula so weight, rather than BMI, is the unknown being solved for.
There's no single "correct" target BMI to enter — the calculator will compute a target weight for whatever figure you choose. Many people pick a value somewhere in the middle of the healthy 18.5–24.9 range, but the appropriate target depends on individual factors such as build, muscle mass, age, and any guidance from a health professional. The tool is designed to show the arithmetic behind a chosen goal, not to prescribe what that goal should be.
Because BMI Prime and target weight are both derived directly from the standard BMI formula, they share every one of the well-known limitations of BMI itself. Neither figure can distinguish muscle mass from body fat, account for frame size, ethnicity, or age, or measure where fat is distributed on the body. Both remain population-level screening figures rather than individual diagnostic tools. For a fuller discussion of these limitations, see this site's BMI Calculator, which covers them in more detail.
What is BMI Prime?
BMI Prime is your standard BMI divided by 25 kg/m², the widely used upper boundary of the WHO "normal weight" category. It expresses BMI as a simple ratio: a BMI Prime under 1.0 means your BMI is below 25, exactly 1.0 means your BMI is exactly 25, and above 1.0 means your BMI is above 25.
How is BMI Prime different from regular BMI?
BMI Prime isn't a different measurement — it's the same BMI number restated as a ratio against the 25 threshold. Regular BMI gives you a kg/m² figure you have to compare against category ranges; BMI Prime gives you a single decimal that already shows how far you are from that boundary, e.g. a BMI Prime of 1.10 means your BMI is 10% above 25.
How do I find my target weight for a specific BMI?
Enter your height and a target BMI into the calculator above. It rearranges the standard BMI formula (weight = target BMI × height in metres squared) to show the exact weight, in kilograms or pounds, that corresponds to your chosen BMI at your current height.
Is a BMI Prime of exactly 1.0 a hard health cutoff?
No. A BMI Prime of 1.0 is simply a mathematical restatement of a BMI of 25 — the conventional line between the "normal weight" and "overweight" WHO categories. It is not a precise individual health cutoff; actual health risk depends on many other factors, and you should not treat crossing 1.0 as a diagnosis.
What target BMI should I choose?
Most people choose a target BMI somewhere within the healthy 18.5–24.9 range, often near the middle (around 21–23), but the right figure depends on your individual circumstances, body composition, and any advice from a health professional. The calculator will compute a target weight for whatever BMI you enter.
Does BMI Prime work for children or teenagers?
No. Like standard adult BMI, BMI Prime and the fixed 25 kg/m² threshold are designed for adults. Children and teenagers should be assessed using age- and sex-specific BMI-for-age percentile charts rather than adult BMI or BMI Prime figures.
Can I use pounds and feet/inches instead of kilograms and centimetres?
Yes. The calculator supports both metric (kilograms and centimetres) and imperial (pounds, feet and inches) units. Switch the unit toggle above the form and the calculator converts your figures internally before applying the BMI Prime and target weight formulas.