BMI Calculation Questions for the NMC CBT

BMI is the only Part A calculation with a square in it, and the square is where every mark is lost. The formula:

BMI = weight in kg ÷ (height in metres)².

Worked example. 70 kg, 1.75 m tall.

• Square the height: 1.75 × 1.75 = 3.0625.
• Divide: 70 ÷ 3.0625 = 22.9.

Do the squaring as its own written step. The error the exam fishes for is dividing by the height once: 70 ÷ 1.75 gives 40, a plausible-looking BMI that’s completely wrong. On the calculator, resist chaining it; get the height squared on screen, note it, then divide.

Centimetres are the other ambush. A height given as 165 cm must become 1.65 m before squaring. The full-mistake version (dividing by 165²) produces an absurd 0.003 and gets caught. The half-mistake, where you convert in your head and square the wrong number, doesn’t announce itself. Write the metres down.

The categories

CBT questions frequently bolt a category onto the calculation, so learn the bands with the boundary numbers:

BMI (kg/m²)	Category
Below 18.5	Underweight
18.5 to 24.9	Healthy weight
25 to 29.9	Overweight
30 and above	Obese

Three boundaries (18.5, 25, 30) carry the whole table. NICE also applies lower action thresholds for some ethnic groups, but numeracy questions use the standard bands; the ethnic-threshold point belongs to Part B health-promotion questions.

BMI also feeds the MUST nutritional screening score, where a BMI under 18.5 scores 2 points and 18.5 to 20 scores 1. The exam likes chaining these: calculate the BMI, then place it in a screening context. If you can do the arithmetic above and hold the bands, the chained version is two easy questions wearing one stem.

Reverse questions

Occasionally the exam runs the formula backwards: what weight gives a BMI of 25 at 1.80 m? Rearrange once and it’s the same arithmetic: weight = BMI × height², so 25 × 3.24 = 81 kg. Nothing new to memorise, just the formula treated as a relationship.

BMI questions are quick marks once the square is habit. Bank them fast in the exam and spend the saved time on multi-step problems later in the paper. Five questions below, then reconstitution and displacement values, which most candidates meet for the first time in CBT prep.