Common Registration Assessment, Part 1
Capping a dose at a stated maximum
Practise weight-based doses where a stated maximum caps the calculated amount, with three original worked questions.
Published 10 October 2026. Independent revision material, not GPhC questions, not for patient care.
Some stems add a maximum dose after the weight-based rate. You calculate the dose from the weight first, then compare it with the cap and give whichever is lower.
The cap can apply to a single dose or to the daily total, so read which one before capping. The examples here are fictional and practise the decision, not any real dosing rule.
The method
- Calculate the weight-based dose or daily total as normal.
- Find the maximum in the stem and note what it applies to.
- Compare the two numbers and take the lower.
- Convert the capped amount to a volume or tablet count if asked.
- Write the capped figure in your answer, not the uncapped one.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
A fictional drug is dosed at 10 mg/kg per day for a patient weighing 68 kg, up to a maximum of 500 mg per day. What daily dose is given?
Show the answer
Answer: 500 mg
Working: Weight-based dose = 10 x 68 = 680 mg, which exceeds the 500 mg maximum. The capped dose is 500 mg per day.
Question 2
A fictional drug is dosed at 2 mg/kg per dose for a patient weighing 85 kg, up to a maximum of 160 mg per dose. What is one dose?
Show the answer
Answer: 160 mg
Working: Weight-based dose = 2 x 85 = 170 mg, which exceeds the 160 mg cap. One dose is 160 mg.
Question 3
A fictional drug is dosed at 15 mg/kg per day in 3 equal doses for a child weighing 12 kg, with a maximum single dose of 50 mg. What is each dose?
Show the answer
Answer: 50 mg
Working: Daily total = 15 x 12 = 180 mg, so 60 mg per dose. The single-dose cap is 50 mg, so each dose is 50 mg.
Circle the word maximum
Underline the maximum and what it applies to before you calculate. It turns the final comparison into a mechanical check instead of a memory test.
Where marks are lost
- Capping the daily total when the maximum applies to a single dose, or the reverse.
- Reporting the calculated dose and ignoring the maximum altogether.
- Applying the cap before finishing the weight-based calculation.
Frequently asked questions
What if the calculated dose is below the maximum?
Give the calculated dose. The cap only bites when the calculation exceeds it.
Can a question have both a single-dose and a daily maximum?
Yes. Check the result against each cap that applies to it and use the lowest figure.
Sources
- The Pharmaceutical Journal, medication maths: using provided formula
- The Pharmaceutical Journal, preparing for the GPhC pharmaceutical calculations assessment
- 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
- Thresholds and dose-banding algorithms
- Unit conversions for mass and volume
- Units and units per mL
- Reconstituting powders and final concentration
- Millimoles and milliequivalents
- Infusion time and volume remaining
- Days supply from pack sizes
- Percentage w/v and w/w conversions
- Ideal and adjusted body weight from formulae
- Diluting creams and ointments by weight
- Scaling a formula to a batch size
- Age-band doses from a provided table
- Tablet fractions and split doses
- Stones, pounds, inches and metric conversions
- Micrograms per minute from mg per hour
- Percentage change and mark-up
- Molar solutions and mass per volume
- Osmolarity from component concentrations
- Direct proportion and cross-multiplication
- Scientific notation and very small quantities
- Stock use and reorder quantities
- Parts per million and very dilute solutions
- Sodium chloride equivalents and isotonic solutions
- Density and specific gravity conversions
- Doses per day and hours between doses
- Finding the volume of diluent to add
- Whole vials and ampoules to draw up
- Reading values from a provided graph
- Micrograms per kg per minute infusions
- Percentage composition of a compound preparation
See also the formula sheet, the eight sample questions and the approved calculator page.