Overweight Calculator

Think of BMI like a debt-to-income ratio for your body — it is a single number that gives a fast, rough read on a complex situation. It does not tell the full story, but it tells enough of the story to be worth knowing before you act.

The calculation divides your weight in kilograms by your height in metres squared. So a person who is 1.75 m tall and weighs 80 kg has a BMI of 80 divided by 3.06, which is 26.1. The scale then maps that number onto four categories: underweight (below 18.5), healthy (18.5 to 24.9), overweight (25 to 29.9), and obese (30 and above). Each category boundary represents a meaningful shift in population-level health risk — not a cliff edge, but a gradient.

The healthy weight range output works backwards from this formula. It takes your height and calculates the minimum and maximum weight that would produce a BMI between 18.5 and 24.9. This is more useful than a raw BMI number because it answers the question most people actually want answered: how far am I from where I should be, in concrete pounds or kilograms?

Use this tool when you want a fast, standardised benchmark to orient yourself before a doctor's appointment, when tracking weight loss progress over time, or when you want to understand what your target weight range actually is in concrete numbers. It is also useful for sanity-checking whether a weight goal you have set for yourself falls within the healthy range or falls short of it.

Do not use this tool as the sole basis for medical decisions. BMI does not diagnose anything — it flags. If your BMI falls outside the healthy range and you have no other symptoms or risk factors, the right next step is a conversation with a GP, not a treatment plan. Similarly, do not use BMI to assess children or teenagers — paediatric weight assessment uses age- and sex-adjusted charts that this tool does not implement.

For people who lift weights regularly, or who are pregnant, or who are recovering from illness, BMI is particularly unreliable. A DEXA scan (dual-energy X-ray absorptiometry) is the most accurate way to measure actual body fat percentage if you need a precise answer. Waist circumference above 88 cm for women or 102 cm for men is a risk indicator that BMI does not capture at all.

The most common mistake is treating the BMI category boundary as a health verdict. A BMI of 25.1 and a BMI of 24.9 are functionally identical in terms of health risk — the line between overweight and healthy is a statistical threshold, not a biological switch. Using it as a pass-fail cutoff causes unnecessary anxiety or false reassurance depending on which side you fall on.

A second mistake is ignoring where you fall within a category. Someone with a BMI of 28 and someone with a BMI of 29.8 are both overweight, but their health profiles and how much change is needed differ meaningfully. The tool shows your distance from the healthy range boundary, not just which bucket you land in — use that number, not just the label.

The third mistake is using BMI to assess athletes, older adults, or people with high muscle mass. A competitive cyclist may have a BMI of 27 with 10% body fat. A sedentary office worker may have a BMI of 23 with 32% body fat. BMI reads the scale; it does not read your body. If your lifestyle or physique differs significantly from a sedentary average adult, treat your BMI as one signal among several rather than the definitive answer.

The BMI formula is: BMI = weight (kg) / height (m) squared. In imperial units, this is converted first: pounds are multiplied by 0.453592 to get kilograms, and inches are multiplied by 0.0254 to get metres. The tool applies these conversions internally so you can enter your numbers in whatever unit you know them.

To find the healthy weight range, the formula is inverted: minimum healthy weight = 18.5 x height(m) squared, and maximum healthy weight = 24.9 x height(m) squared. For a person who is 5 ft 9 in (1.753 m), this gives a range of 56.8 kg to 76.5 kg, or roughly 125 lb to 169 lb. The weight-to-lose figure is your current weight minus 24.9 x height(m) squared — the top boundary of healthy.

One thing this formula cannot do is account for body composition. Two people with identical height and weight produce identical BMIs, even if one is 15% body fat and the other is 35% body fat. This is the core limitation of any weight-divided-by-height-squared metric. It was designed as a population screening tool, not as a way to assess an individual's body fat percentage.

The BMI formula assumes a specific relationship between height and weight that breaks down at the extremes of height. Very tall people (above 6 ft 3 in or 190 cm) tend to have their BMI overestimated — they read heavier on the scale relative to their actual fat mass — while very short people tend to have their BMI underestimated. This is a known mathematical artefact of the squared-height denominator. Some clinicians use adjusted BMI formulas for patients above 195 cm, though no single adjusted formula is universally adopted. If your height is at the extremes, treat your result as directionally correct but not precise.