Common Registration Assessment, Part 1
Rounding rules in calculations
Many lost marks come from rounding at the wrong point. Three original questions on when to round and when to leave a number alone.
Published 5 October 2026. Independent revision material, not GPhC questions, not for patient care.
The Pharmaceutical Journal's guide to rounding makes a point that is easy to miss: if a registration assessment question has no rounding instruction at the end, the correct worked answer is already a whole number. If your answer is not whole, something has gone wrong and the question needs another attempt.
The guide also says some questions need rounding in the middle, for example a dose that has to be a measurable volume, and that the rule is simple: 5 or above rounds up, below 5 rounds down. The questions here are original and practise those three situations.
The method
- Look for a rounding instruction at the end and in the scenario itself.
- If there is none, expect a whole-number answer and recheck your working if you do not get one.
- Round in the middle only when the scenario says a dose must be a measurable amount, such as whole mL or whole capsules.
- Use the rounded figure in every step after that, then check the answer is sensible.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
A patient weighing 58 kg is prescribed 250 units/kg daily for 12 days. How many units are given in the course? (No rounding instruction is given.)
Show the answer
Answer: 174000 units
Working: 250 × 58 = 14,500 units a day. 14,500 × 12 = 174,000 units. The answer is a whole number, which fits the fact that the question has no rounding instruction. Enter it without commas.
Question 2
A child weighing 17 kg is prescribed 300 micrograms/kg twice daily. The suspension is 10 mg in 5 mL, and each dose is to be rounded to the nearest whole mL. How many mL are needed for 10 days?
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Answer: 60 mL
Working: 17 × 300 = 5,100 micrograms = 5.1 mg. 5.1 mg ÷ 2 mg/mL = 2.55 mL, which rounds to 3 mL because the digit is 5. 3 mL × 2 doses × 10 days = 60 mL. The rounding comes in the middle, so the later steps use 3 mL, not 2.55 mL.
Question 3
A cytotoxic medicine is prescribed at 25 mg/m² daily for 3 days. The patient is 168 cm tall and weighs 82 kg, and capsules are 20 mg. Work out BSA with √(height in cm × weight in kg ÷ 3600) and round each daily dose to the nearest whole capsule. How many capsules are needed for the course?
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Answer: 6 capsules
Working: BSA = √(168 × 82 ÷ 3600) = √3.827 = 1.956 m². Daily dose = 25 × 1.956 = 48.9 mg, which is 2.45 capsules, so 2 capsules a day. 2 × 3 = 6. The patient cannot take part of a capsule, so the rounding is done before the course total.
What the rounding guide says
The guide's worked examples include a clobazam suspension where each dose of 2.375 mL is rounded to 2 mL before multiplying by two doses a day for 14 days, and a cytotoxic dose where a daily 42 mg is rounded to 40 mg because the capsules are 20 mg. The questions on this page use different drugs and numbers.
Where marks are lost
- Rounding at the end when the scenario asks for rounding of each dose first.
- Keeping a long decimal after the question has said each dose is rounded.
- Adding commas or units in the answer box when the answer is a plain number.
Frequently asked questions
What if my answer is not a whole number and there is no instruction?
The guide says the answer is wrong and the question should be attempted again. Check units, the number of doses and the number of days.
Which way does 2.5 round?
Up. A figure of 5 or above rounds up, and anything below 5 rounds down.
Sources
- The Pharmaceutical Journal, a guide to rounding for pharmacy students and trainees (27 October 2021)
- GPhC, Common Registration Assessment specification and permitted items for 2026
The questions above are original and use fictional drugs. PreRegExamPrep is not affiliated with or endorsed by the General Pharmaceutical Council.
Practise until the method is automatic
Try 15 free questions with worked answers. No sign-up required.
More calculation topics
- Dose by weight calculations for the GPhC assessment
- Volume to give: liquid medicine calculations
- Percentage strength calculations: w/v, w/w and ratios
- Dilution calculations with C1V1 = C2V2
- Infusion rate calculations in mL per hour
- Drip rate calculations: drops per minute
- Body surface area calculations
- Creatinine clearance (Cockcroft-Gault) calculations
- Moles and millimoles calculations
- Displacement volume calculations for reconstitution
- Quantity to supply calculations
- Using a provided formula in calculations
- Dose information from packaging and labels
- Diluting a stock to a lower strength
- Medicine cost and switch calculations
- Enteral feed rate calculations
- Electrolyte content over time
- Infusion dose per kg per hour
- Rounding doses to measurable volumes
See also the formula sheet, the eight sample questions and the approved calculator page.