BMI calculator

Your BMI, and then the part most calculators leave out: an honest account of what this number can and can't tell you about your body.

Milo

Sex

Weight (kg)

Height (cm)

Your BMI will appear here.

How this is worked out

BMI is your weight divided by your height squared. That’s the whole formula, and it’s worth sitting with how little goes into it:

BMI = weight(kg) ÷ height(m)²

It was devised in the 1830s by a Belgian statistician studying populations, not patients. It was never intended to assess an individual, and Quetelet said as much. Across thousands of people it correlates usefully with health outcomes; applied to you specifically, it’s a blunt instrument.

The three ways it misleads. It can’t see muscle, so it labels plenty of strong, lean people overweight or obese. It’s a ratio of weight to height squared, while people scale closer to height cubed, so it reads high on short people and low on tall ones. And it says nothing about where fat sits, which is what actually predicts risk.

Better numbers, if you want them: your waist measurement, your waist-to-height ratio, which ideally sits under 0.5, and your body fat percentage from a tape measure. All three beat BMI for an individual, and none is harder to get.

The number is the easy part

Any calculator can hand you a figure. The hard bit is the next three months: eating roughly to it, noticing when it stops working, and changing it. Milo is a coach you text like a friend. You log what you ate in a sentence, and it learns your patterns, notices when your weight stalls, and adjusts the target from what you actually did rather than from a formula.

See how Milo works

Common questions

Is BMI useless then?

Not useless, just misapplied. At population scale it’s a reasonable screening tool and it’s cheap, which is why doctors still use it. As a description of one person’s health it’s weak, and it should never be the only thing you look at.

My BMI says overweight but I lift. Should I worry?

Probably not on the strength of BMI alone. Muscle is denser than fat, and a trained person can sit well into the overweight band at a low body fat percentage. Check your waist and your body fat percentage instead.

Does BMI work differently for different ethnicities?

Yes. Risk thresholds are lower for people of South Asian, Chinese and other Asian backgrounds, where health problems appear at BMIs the standard chart calls healthy. Several health bodies use adjusted cut-offs for exactly this reason.

What should I track instead?

Your waist, measured the same way each month, and the direction your weight is trending over weeks rather than days. Both tell you more about what’s changing than a BMI recalculated from the same two numbers.

Other calculators

Body fat calculator — Your body fat percentage from a tape measure, no calipers needed.
Lean body mass calculator — How much of your weight isn't fat, and why it matters.
Waist-to-height ratio — The one-line check that beats BMI: waist under half your height.
TDEE calculator — How many calories you burn in a day, and what to eat for your goal.
Calorie deficit calculator — How long a given deficit takes to reach your goal weight.

These are estimates from population averages, not measurements of you. Individual metabolism varies by roughly ±10% around any formula. Nothing here is medical advice — if you have a health condition, are pregnant, or are under 18, talk to a healthcare professional before changing how you eat or train.