NHS recruitment uses numeracy assessments at multiple stages — at application, at interview, and as part of the NMC CBT for nurses. They're not designed to catch you out, but they reward speed and accuracy under pressure. This guide covers the four calculation types you'll see most.
Drug calculations: the universal formula
Whatever the question, drug calculations come down to one formula:
(Required dose ÷ Stock dose) × Stock volume = Volume to give
Example: A patient is prescribed 75 mg of pethidine. Stock vials contain 100 mg in 2 ml. How much do you give? (75 ÷ 100) × 2 = 1.5 ml.
IV infusion rate (drops per minute)
(Volume × Drop factor) ÷ Time in minutes = Drops per minute
Example: 1000 ml of saline over 8 hours, drop factor 20. (1000 × 20) ÷ 480 = 41.6, round to 42 drops per minute.
mg per kg dosing for paediatrics
Required dose per kg × Weight in kg = Total dose
Example: A child weighing 18 kg needs paracetamol at 15 mg/kg. 15 × 18 = 270 mg.
Percentages
Two shortcuts that save time:
- 10% is just dividing by 10. 25% is half of 50%. 75% is 50% + 25%.
- To find what percentage A is of B, do (A ÷ B) × 100.
Common pitfalls
- Decimal places — 0.25 mg is very different from 2.5 mg. Always sense-check.
- Unit conversion — 1 g = 1000 mg, 1 mg = 1000 micrograms (mcg). Convert before calculating.
- Time conversion — IV rates are usually in minutes. Convert hours to minutes first.
- Rounding — round only at the end, and only to the nearest whole drop or millilitre as the question requires.
Calculator or no calculator?
The NMC CBT does not allow calculators. Many local NHS trust assessments do allow one. Always check the rules in your invitation letter — and practise both with and without so you're ready either way.
Mental maths shortcuts
Memorise the times tables up to 12, learn to halve and double quickly, and practise dividing by 10 and 100 by moving the decimal point. These three skills cover 80% of NHS calculation questions.
Practice plan
Aim for 20 minutes a day for two weeks. Take one full mock every other day, and use the alternating days to drill any specific calculation type you got wrong. By day 14 you should be answering most questions inside 60 seconds.
Try a free NHS numeracy mock
Take our free NHS Numeracy practice test now to baseline your score. The full NHS & Healthcare hub also covers literacy, values-based recruitment and the NMC CBT for overseas nurses.
