Common Registration Assessment, Part 1
Tablet fractions and split doses
Practise working out fractions of a tablet and how many tablets are needed for a course, with three original questions.
Published 9 October 2026. Independent revision material, not GPhC questions, not for patient care.
A dose is sometimes a fraction of a tablet, such as half or three quarters. The arithmetic is dose divided by tablet strength, followed by multiplying by doses per day and days.
These examples are fictional. They practise the arithmetic only; they do not say a tablet can be split. A real tablet needs to be suitable for splitting first.
The method
- Divide the dose by the tablet strength to find the fraction of a tablet.
- Multiply by doses per day to find tablets per day.
- Multiply by the number of days for the course total.
- Round up to a whole tablet only at the end if the question asks for whole tablets supplied.
- Check the fraction is one the question allows, such as a half.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
A fictional dose is 37.5 mg. Scored tablets are 75 mg. What fraction of a tablet is one dose?
Show the answer
Answer: Half a tablet
Working: 37.5 ÷ 75 = 0.5.
Question 2
A fictional dose is three quarters of a 20 mg tablet once daily for 28 days. How many tablets are needed?
Show the answer
Answer: 21 tablets
Working: 0.75 × 28 = 21 tablets. The dose itself is 15 mg.
Question 3
A fictional dose is 12.5 mg twice daily from 25 mg tablets for 14 days. How many whole tablets are needed?
Show the answer
Answer: 14 tablets
Working: Per dose = 0.5 tablet. Per day = 1 tablet. 14 days need 14 tablets.
Fraction first
Convert the dose to a fraction of a tablet, then handle days. It keeps the working in tablets throughout.
Where marks are lost
- Counting each half as a whole tablet.
- Forgetting doses per day.
- Rounding up the daily amount instead of the course total.
Frequently asked questions
Why round only at the end?
Rounding each day separately can over-count. The course total is the amount you supply.
Is every tablet suitable for splitting?
No. This is arithmetic practice only; the question has to state that splitting is allowed.
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
- 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
See also the formula sheet, the eight sample questions and the approved calculator page.