Common Registration Assessment · Topic deep-dive
GPhC Calculation Rounding Rules
Rounding is the single most-flagged pitfall in CRA Part 1. The Board of Assessors has named it in both the June 2025 and November 2025 feedback documents. The rule is not “always round at the end” — it depends on whether you are calculating a single dose, a quantity to supply, or a rate. This page walks through every rounding pattern the GPhC tests.
What the GPhC actually tests on this topic
- When to round mid-calculation (e.g. rounding individual doses before totalling supply) vs at the end
- Round up vs round down — the practical judgement, including matching to oral syringe graduations
- Rounding rules instructed in the stem: “to one decimal place”, “to the nearest mL”, “to the nearest tablet”
- Dosage-form constraints: capsules not divisible, ampoules single-use, scored vs unscored tablets
- Final-volume safety checks: does the rounded answer give an administrable dose?
Common pitfalls — from the Board of Assessors’ feedback
Rounding at the wrong stage of the calculation
The June 2025 feedback explicitly notes: “when calculating the total amount of a medicine that should be supplied, rounding should occur for an individual dose before calculating a final amount.” This is the most common error. If a single dose rounds from 7.2 mL to 7.5 mL (the nearest syringe graduation), the total supply uses 7.5 mL per dose, not 7.2 mL.
Rounding decimals instead of graduations
For oral liquids supplied with an oral syringe, the Board of Assessors notes candidates should round to the available graduation marks on the syringe — not to two decimal places. If the syringe is 5 mL with 0.2 mL graduations, the rounded answer must be a multiple of 0.2.
Forgetting dosage-form constraints
A patient cannot take part of a capsule, and ampoules are single use. If the maths gives you 1.6 capsules, you cannot dispense that — you round to the practical dose (2 capsules) or refer back to the prescriber depending on the clinical scenario.
Ignoring the explicit rounding instruction
When the stem says “give your answer to the nearest mL” or “to one decimal place”, that is your rounding instruction. Always read the answer-format instruction last so it is fresh in your mind when you commit your final answer.
Sample calculation questions
CRA-style practice questions, not real exam questions. The Board of Assessors does not endorse third-party question banks.
A 62 kg patient with an eGFR of 8 mL/min/1.73m² is prescribed amikacin at 15 mg/kg once daily. The BNF recommends a maximum single dose of 1500 mg and the following renal dose adjustments: eGFR 0-14 mL/min/1.73m²: reduce to 25% of normal dose. Amikacin injection is available as 50 mg/mL in 2 mL vials. What is the correct amikacin dose for this patient?
- A. 232.5 mg
- B. 465 mg
- C. 58.12 mg
- D. 77.42 mg
- E. 2325 mg
Show worked answer
Correct answer: A
A patient is started on carbamazepine for epilepsy — initiation using the following titration schedule: 100 mg twice daily for 7 days; 200 mg twice daily for 7 days; 300 mg twice daily for 14 days; 400 mg twice daily for 28 days. Carbamazepine is available as 100 mg tablets. Tablets come in packs of 84. How many packs should be dispensed for the primary drug?
- A. 1.67 pack(s) of 84
- B. 5 pack(s) of 84
- C. 3.33 pack(s) of 84
- D. 10 pack(s) of 84
- E. 20 pack(s) of 84
Show worked answer
Correct answer: B
Rounding in calculations — frequently asked
When should I round mid-calculation vs at the end?
Round mid-calculation when the rounded value is what will physically be dispensed or administered (e.g. an individual dose to a syringe graduation, then totalled for supply). Round only at the end when the question asks for a single final value (e.g. an infusion rate). The Board of Assessors flagged this as the most common Part 1 error.
Should I always round up?
No. You round to the practical, administrable quantity. For oral liquids, round to the syringe graduation provided in the stem. For tablets and capsules, round to the practical whole quantity unless the tablet is scored. For supplies that must cover a treatment duration, you may round up to ensure the patient has enough — but never to a quantity that exceeds a stated maximum dose.
How do I know what to round to?
Three signals to check, in this order: (1) the rounding instruction in the stem (“to one decimal place”), (2) the dosage form (capsule, ampoule, syringe graduation), and (3) the clinical practicality (administrable, available stock quantity). If two signals conflict, the explicit stem instruction wins.
Are rounding rules different for paediatric calculations?
The principles are the same but the constraints are tighter. Paediatric doses often need to fit a 1 mL or 2.5 mL oral syringe with finer graduations (0.05 mL or 0.1 mL). Always check BNFC maximum doses against your rounded value — rounding up over the maximum dose is a clinical error the Board of Assessors specifically warns against.
Practise rounding in calculations questions in context
Across the full bank of GPhC exam questions — every format, with worked answers grounded in the Board of Assessors’ published feedback.