Many candidates find calculations the most anxiety-inducing CRA component. The anxiety is understandable — numerical answers are either right or wrong, with no partial credit for clinical reasoning. The remedy is daily practice. Even 10 minutes per day builds the confidence and accuracy that eliminates calculation anxiety by exam day.
Calculation Types
Dosing. Dose per kilogram (mg/kg), daily dose calculations, loading and maintenance doses. Dilutions. Concentration changes, serial dilutions, diluting stock solutions to working concentrations. Displacement values. Reconstitution of powders, suppository displacement calculations — a topic many candidates find unfamiliar. Infusion rates. ml/hour from dose per minute/hour, drops per minute using standard giving sets. Unit conversions. mg to g, mmol to mg, percentage solutions to mg/ml, micrograms to milligrams. Moles and millimoles. Concentration calculations using molecular weights.
Systematic Approach
Write the formula. Substitute the values with units. Check that units cancel correctly (dimensional analysis). Calculate. Sense-check the answer — is a 5,000mg dose of paracetamol for an adult reasonable? If the answer seems implausible, re-check.
Most Common Errors
Unit conversion mistakes — the single most frequent calculation error. Confusing mg and g, ml and L, micrograms and milligrams. Decimal point misplacement — leading to 10x errors (500mg instead of 50mg). Not accounting for displacement in suppository calculations. Rounding errors — not following the expected rounding convention for the answer type.
Practice Strategy
Do calculations daily — even 10 minutes. Start with simple dosing calculations and progress to complex infusion rates and displacement. Time yourself: aim for 2-3 minutes per calculation, matching exam pace. Build a personal bank of 50+ worked examples covering each calculation type. Review errors carefully — understand why you went wrong, not just what the right answer was.
What Is Allowed
An on-screen calculator is provided during the exam. Practise using it efficiently — the maths is not complex, but speed and accuracy under time pressure require familiarity with the tool.