Common Registration Assessment, Part 1
Percentage change and mark-up
Practise percentage increase, mark-up on cost and working back to the original price, with three original worked questions.
Published 9 October 2026. Independent revision material, not GPhC questions, not for patient care.
Pharmacy calculations include money as well as dose. A percentage change is the change divided by the original value, multiplied by 100. A mark-up is a percentage added to the cost price.
The prices below are fictional. The key habit is to work out which number is the base before you calculate the percentage.
The method
- Identify the base value, which is the original or cost price.
- For change, subtract original from new, divide by original, then multiply by 100.
- For mark-up, multiply cost by 1 plus the percentage as a decimal.
- To work back, divide the selling price by 1 plus the mark-up.
- Give money to two decimal places.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
A fictional price rises from £12.50 to £14.00. What is the percentage increase?
Show the answer
Answer: 12%
Working: Change = £1.50. 1.50 ÷ 12.50 = 0.12, so 12%.
Question 2
A fictional item costs £8.00 and is sold with a 35% mark-up. What is the selling price?
Show the answer
Answer: £10.80
Working: 8.00 × 1.35 = £10.80.
Question 3
A fictional selling price is £15.60 and includes a 30% mark-up on cost. What was the cost price?
Show the answer
Answer: £12.00
Working: Cost = 15.60 ÷ 1.30 = £12.00.
Name the base
Write base = original price beside every percentage. Most errors are the wrong base.
Where marks are lost
- Dividing the change by the new price instead of the original.
- Subtracting 30% from the selling price to find cost.
- Rounding money before the final step.
Frequently asked questions
Why not subtract 30% from £15.60?
The mark-up is 30% of the cost, not of the selling price, so you divide by 1.30.
Is mark-up the same as profit margin?
No. Mark-up is based on cost, margin on selling price. Use the definition in the question.
Sources
- The Pharmaceutical Journal, medication maths: quantities to supply and using provided formulae
- 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
- 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
See also the formula sheet, the eight sample questions and the approved calculator page.