The most useful calculation resource is the one that helps you correct your particular error: extracting the wrong information, mixing units, choosing the wrong relationship, making an arithmetic slip or entering the answer incorrectly. Start by identifying that error, then practise in the format required by your own assessment.
iatroX publishes this calculation-resource comparison and includes its PSA and GPhC pathways. The recommendations match practice to the learner's error while keeping the two professional assessments distinct. Product descriptions and resource availability throughout are dated 6 September 2026.
The Prescribing Safety Assessment and the GPhC Common Registration Assessment are different examinations for different professional pathways. Shared arithmetic does not make their preparation resources interchangeable.
Start with the official task
The Prescribing Safety Assessment website describes the assessment's question types and preparation arrangements. Calculations form one part of a broader assessment. A resource devoted to arithmetic should therefore supplement, rather than replace, practice across the other required activities.
For pharmacy candidates, use the GPhC's current Common Registration Assessment information and the instructions for your sitting. Part 1 uses numerical free-entry questions. Recognising the nearest option in a multiple-choice exercise is not the same activity as producing and entering a number yourself.
Before buying, establish which component a product covers, how answers are entered and what explanations accompany errors. "Calculation questions included" is not enough detail to assess its suitability.
Classify errors before increasing question volume
Review a small selection of recent attempts with your working visible. Do not label every mistake as "bad at maths". The label provides no indication of what should change next.
| Error type | What happened | Useful practice |
|---|---|---|
| Information extraction | A relevant quantity or instruction was missed | Mark quantities and requested output before calculating |
| Unit handling | Values were combined in incompatible units | Conversion exercises with explicit unit cancellation |
| Relationship selection | The wrong quantities were multiplied or divided | Explain the relationship before inserting numbers |
| Arithmetic | The setup was sound but the calculation was wrong | Short checks and independent recalculation |
| Rounding or entry | A correct result was presented incorrectly | Practise the assessment's stated instructions |
Keep categories provisional. One mistaken answer can involve more than one problem, and a single slip does not establish a persistent weakness.
A worked example without a drug calculation
Consider an original stock-planning exercise: a teaching room needs 42 disposable items, and each sealed box contains seven. How many boxes are required?
The requested output is boxes, not individual items. The relationship is 42 items divided by seven items per box, producing six boxes. Writing the units makes the reasoning visible: items cancel, leaving boxes.
Now change the required stock to 43 items while keeping seven per sealed box. The arithmetic produces just over six, but the context requires seven whole boxes. This is not an instruction to round every examination answer upwards; it illustrates why the requested output and context determine how a result should be presented.
A separate non-clinical exercise, converting 0.75 metres to 75 centimetres, tests another skill. A learner who can do that conversion may still choose the wrong relationship in a longer question. Practise the specific difficulty rather than treating all calculation items as equivalent.
What a good explanation should contain
Look for the path from the question to the result: relevant information, compatible units, the relationship used, the calculation and the interpretation of the output.
A bare worked equation may be insufficient when your difficulty is understanding why that equation applies. Conversely, a long conceptual explanation may be unnecessary when the only problem is repeatedly transcribing a number incorrectly.
Sample an incorrect attempt deliberately. Does the resource help distinguish your method from the intended one? Can you identify the first point at which the reasoning diverged? Does it explain a rounding convention only where the question actually requires it?
Prefer these observable qualities to broad promises about eliminating mistakes. No resource can establish competence merely by displaying a completed calculation on screen.
Combine untimed method work with realistic practice
Use untimed exercises while rebuilding a relationship you do not understand. State the output unit first and explain the setup before calculating. Once that method is clear, introduce timed practice appropriate to the examination.
For a free-entry assessment, conceal answer options where possible and produce the number independently. This is an additional exercise, not a claim that hiding options perfectly recreates the official interface. Use official familiarisation material for the actual response process.
For PSA preparation, retain practice across the wider assessment rather than allowing a rewarding sequence of arithmetic successes to displace other tasks. For pharmacy preparation, check the current sitting guidance for permitted equipment and instructions rather than relying on an old course handout.
A useful weekly review asks which error category is recurring. The answer should determine the next session, not an arbitrary target to complete another hundred calculations.
How iatroX can support the learning
As published on 6 September 2026, the iatroX examination catalogue includes a free PSA question bank and a paid GPhC assessment pathway. Choose the appropriate route; do not assume that questions written for medical students provide complete pharmacy assessment preparation.
The Socratic Tutor is useful when you need to explain the method behind an answer. For example, a session can focus on why the requested unit requires division rather than multiplication, instead of asking only for the final result. Study planning can help reserve recurring practice for a weakness that otherwise gets overlooked.
Check the available question and response formats against your official assessment requirements. A bank's educational value does not mean that every item reproduces the examination interface or that a subscription replaces official familiarisation.
As published on 6 September 2026, iatroX's UK pricing is £99 a year, paid upfront, equivalent to £8.25 a month billed annually, or £29 a month. The paid subscription includes question banks, Socratic Tutor, the study planner, iatroX Simulations and CPD tools together; simulations and CPD are not separate add-ons.
The September 2026 free offering is separate from the subscription: Ask-iatroX and free question access have no trial expiry or verification gate. Free samples and designated free banks should not be confused with unlimited access to every paid bank or ongoing tutoring.
Which resource fits your preparation?
Choose worked method teaching when units or relationships are unclear, official profession-specific material for assessment expectations, and timed practice once the method is secure. iatroX can support the relevant question and tutoring pathway, but PSA and GPhC candidates should not treat each other's banks as complete substitutes.
Frequently asked questions
Should every calculation error lead to more timed questions?
No. First identify whether the problem is interpretation, units, the mathematical relationship or presentation of the result, then practise that step without unnecessary time pressure.
Can PSA questions replace GPhC assessment preparation?
No. Some calculation skills transfer, but candidates need resources aligned with their own profession's assessment and current instructions.
Why use a non-clinical worked example?
It isolates the mathematical reasoning without suggesting a clinical dose or treatment instruction. Once the method is clear, use authorised examination material for profession-specific practice.