Common Registration Assessment, Part 1
Thresholds and dose-banding algorithms
Follow supplied dose bands, maximum caps and rounding steps, with three fictional calculation algorithms.
Published 7 October 2026. Independent revision material, not GPhC questions, not for patient care.
A dose-banding problem combines arithmetic with a decision rule. The calculation can be right and the answer wrong if you choose the wrong side of a threshold. Circle less than, at least and greater than.
Use the resource’s order of operations. If it says cap before rounding, do that; if it says choose a band from the unrounded value, do not round first. These fictional algorithms are revision exercises, not actual dosing guidance.
The method
- Calculate the input without premature rounding.
- Compare it with the thresholds.
- Check which band includes the exact boundary.
- Apply the selected formula and cap in the stated order.
- Round only at the instructed step.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
A fictional algorithm assigns 100 mg for a score below 50, and 150 mg for a score at least 50. Score = weight in kg × 0.8. Weight is 62.5 kg. Which dose is assigned?
Show the answer
Answer: 150 mg
Working: Score = 62.5 × 0.8 = 50. Equality belongs to the at-least-50 band, assigning 150 mg.
Question 2
Calculate 7 mg/kg for a fictional 68 kg patient. Apply a maximum of 450 mg, then round to the nearest 25 mg. Find the answer.
Show the answer
Answer: 450 mg
Working: Raw amount = 476 mg. Cap at 450 mg, already a multiple of 25 mg.
Question 3
Choose a band from the unrounded value: below 100 mg gives 80 mg; at least 100 but below 200 mg gives 160 mg; at least 200 mg gives 240 mg. Value = 2.5 mg/kg × 79.8 kg. Find the banded dose.
Show the answer
Answer: 160 mg
Working: Value = 199.5 mg, at least 100 and below 200. Assign 160 mg. Rounding to 200 first would select the wrong band.
Trace the path
Beside each line, write which rule you used. The Pharmaceutical Journal worked algorithm shows why reference-based questions need both calculation and rule-following. These original examples practise that skill without reproducing its clinical conversion.
Where marks are lost
- Rounding before a band defined on unrounded values.
- Treating at least as greater than.
- Applying a cap to an intermediate step instead of the final amount.
Frequently asked questions
What happens at an exact boundary?
Read the rule. At least includes equality; less than excludes it. A rule without a defined boundary is incomplete.
Can I reorder the steps?
No. A cap, reduction, band choice and rounding may give different answers in another order.
Sources
- The Pharmaceutical Journal, medication maths: using provided formula
- GPhC, 2026 assessment specification and permitted items
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
- Rounding rules in calculations
- Enteral feed rate calculations
- Electrolyte content over time
- Infusion dose per kg per hour
- Rounding doses to measurable volumes
- Relative risk and relative risk reduction
- Absolute risk reduction and number needed to treat
- Odds ratio and confidence intervals
- Relative versus absolute risk reduction
- Loading dose and volume of distribution
- Top-up doses from measured drug levels
- Salt correction factors
- Mass and molar drug concentrations
- Half-life and falling drug levels
- Steady-state concentration and infusion rate
- Bioavailability and equivalent oral doses
- Oral maintenance dose and dosing interval
- Elimination rate constant and half-life
- Accumulation towards steady state
- Ratio strengths and one in X
- Serial dilution factors
- Mixing solutions of different strengths
- Tablet quantities for reducing regimens
- Equivalent doses from provided conversion tables
See also the formula sheet, the eight sample questions and the approved calculator page.