Common Registration Assessment, Part 1
Stock use and reorder quantities
Practise working out days of stock left and how many packs to reorder, with three original worked questions.
Published 9 October 2026. Independent revision material, not GPhC questions, not for patient care.
Pharmacy stock calculations use average daily use. From daily use you can find how many days of stock remain and how much to order to cover a period.
The figures are fictional. The method is division, then rounding to whole packs at the end.
The method
- Find average daily use by dividing total used by the days.
- Divide current stock by daily use for days remaining.
- For an order, multiply daily use by days to cover, then subtract stock.
- Divide by pack size and round up to a whole pack.
- Check the order covers the period.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
A fictional product has a lead time of 3 days and a safety margin of 2 days. Daily use is 6 packs. What is the reorder level?
Show the answer
Answer: 30 packs
Working: Cover needed = 3 + 2 = 5 days. 5 × 6 = 30 packs.
Question 2
A fictional tablet uses 420 tablets over 28 days. What is the average daily use?
Show the answer
Answer: 15 tablets
Working: 420 ÷ 28 = 15 tablets per day.
Question 3
Stock is 200 tablets, use is 15 a day and packs hold 28 tablets. How many packs are needed to cover 28 days?
Show the answer
Answer: 8 packs
Working: Total need = 420. Order = 420 - 200 = 220 tablets. 220 ÷ 28 = 7.86, so 8 packs, which is 224 tablets.
Days is the link
Convert stock to days of cover. It turns every question into the same comparison.
Where marks are lost
- Rounding down when whole packs are needed.
- Forgetting to subtract current stock.
- Using the wrong number of days.
Frequently asked questions
Why round up?
You cannot order part of a pack, and rounding down leaves a shortfall.
What is a safety margin?
Extra days of stock held in case of delay or a rise in use.
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
- 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
See also the formula sheet, the eight sample questions and the approved calculator page.