In November 2024, nearly 1 in 3 candidates failed Part 1 of the GPhC registration assessment. In June 2025, 16% failed — better, but still meaning that for every six candidates, one failed Part 1 and wasted their entire sitting regardless of how well they performed on Part 2.
Part 1 is 40 questions in 120 minutes. That is 3 minutes per question. With a calculator you are allowed to bring. And yet the pass rate remains stubbornly imperfect because the exam tests calculation types under time pressure — not mathematical ability in isolation.
This article is a complete Part 1 strategy guide: what you will face, how to drill it, and how to use adaptive tools to close the gaps specific to you.
What Part 1 Actually Tests
Part 1 is closed book: 40 numerical free-entry questions where you type the number, not select from options. There is no partial credit and no negative marking. The pass mark in June 2025 was 24 out of 40.
Dose and Dose Regimen Calculations
Simple unit dose, multiple dose, frequency adjustments. The CRA uses various dose expressions — definite frequency (e.g., 500mg every 8 hours, 2.5mg/kg twice daily) and total daily dose format (e.g., 150mg/kg/day in 3 divided doses).
Worked example: Patient weighs 68 kg, dose is 5mg/kg twice daily. Single dose = 5 × 68 = 340mg. 24-hour dose = 340 × 2 = 680mg.
Unit Conversions
mg to mcg, g to mg, mL to L, mmol to mg. The dangerous conversions are micrograms to milligrams — tenfold errors in this conversion cause real patient harm, and the exam specifically tests whether you can navigate them accurately.
Worked example: Convert 250 micrograms to milligrams. 250 ÷ 1000 = 0.25mg.
IV Infusion Rates
mL/hour, drops/minute, infusion duration. The Board of Assessors feedback specifically notes that candidates should consider all relevant information in the scenario when calculating IV infusion rates — infusion time, concentration, and rate.
Worked example: 1000 mL over 8 hours. Rate = 1000 ÷ 8 = 125 mL/hour.
Displacement Values
Reconstitution of powders for injection. If you ignore displacement volume, you calculate a wrong dose. The Board of Assessors feedback states that candidates are expected to apply pharmaceutical principles to the preparation of medicines, including displacement volumes and values when reconstituting powder.
Worked example: Amoxicillin 250mg/5mL suspension. Displacement value is 0.2mL per 250mg vial. To make 5mL final volume, add 5 - 0.2 = 4.8mL of water.
Concentration Expressions
%w/v, %w/w, 1:x ratios, parts per million, molarity. These are the expressions candidates find most conceptually challenging.
Worked example: What is the concentration of a 1:1000 adrenaline solution in mg/mL? 1:1000 means 1g in 1000mL = 1000mg in 1000mL = 1mg/mL.
Creatinine Clearance and Renal Dose Adjustments
Cockcroft-Gault equation — know it by heart: CrCl = [(140 - age) × weight × constant] / serum creatinine. Apply the calculated CrCl to BNF dose reduction thresholds. The constant is 1.23 for males and 1.04 for females.
Paediatric Weight-Based Dosing
Age- and weight-appropriate calculations using BNF for Children dosing conventions.
Worked example: Child weighs 22 kg, dose is 10mg/kg. Total dose = 10 × 22 = 220mg. If available preparation is 125mg/5mL, volume = (220/125) × 5 = 8.8mL.
Why Candidates Fail Part 1 (and How to Avoid It)
Failure mode 1: Practising without a timer. In exam conditions, pace matters as much as method. If you practise calculations untimed, you are not preparing for the real exam.
Failure mode 2: Practising one type repeatedly and neglecting others. Displacement values and molarity are the most commonly underprepared calculation types. Candidates drill the types they find comfortable and avoid the ones they find confusing — exactly the wrong approach.
Failure mode 3: Calculator unfamiliarity. If you are using the on-screen Surpass calculator for the first time on exam day, you will lose time navigating the interface. Practise with your actual exam calculator from day one.
Failure mode 4: Rounding errors. The Board of Assessors feedback specifically addresses rounding — noting that sometimes rounding should occur at intermediate stages, sometimes only at the end. For oral liquids, consider the graduation marks on the supplied syringe. When instructions specify "give your answer to one decimal place," follow them exactly.
How iatroX addresses this: The adaptive engine tracks your accuracy and speed across each calculation type independently. If you are fast and accurate on IV rates but slow on displacement values, the engine concentrates your practice on displacement — not a pre-set rotation. Difficulty scales as you improve within each type, ensuring you are always working at the edge of your competence.
The iatroX Part 1 Approach — Adaptive Calculations
Standard revision: you work through a calculation bank in sequence or by topic. You see each question once. You get them right or wrong. You move on.
Adaptive revision with iatroX: the engine identifies which calculation types you are slowest or least accurate on and serves more of those, increasing difficulty as you improve. The performance dashboard shows accuracy AND speed by calculation type — because Part 1 is a time-pressure exam where knowing the method is insufficient without the pace.
Mobile access means you can drill calculations on your phone between dispensing sessions during your foundation year. Available at iatrox.com/boards.
A 4-Week Part 1 Intensive Plan
Week 1: Audit and baseline. Work through one set of each calculation type. Note which take longest and which you get wrong. Use iatroX diagnostic mode to establish your baseline proficiency across all calculation types.
Week 2: Systematic drilling. 30 minutes per day, two calculation types per day, all timed. Focus on your weakest types from the Week 1 audit. Use iatroX adaptive sets for precision targeting.
Week 3: Mixed-type timed mock sets. Simulate exam conditions — 40 questions, 120 minutes. Review every error. Check rounding conventions. Verify that your calculator technique is efficient.
Week 4: Targeted weak-area consolidation. Use iatroX adaptive sets concentrated on your remaining weak calculation types. Final full mock under exam conditions. Review the Board of Assessors feedback on Part 1 from the most recent sitting.
Calculator Strategy
You can bring your own calculator — but only GPhC-approved makes and models. Non-approved calculators are confiscated at the test centre. Check the current approved list on the GPhC website well before exam day.
Use the same calculator for all practice from month one. If you plan to use the on-screen Surpass calculator, access it in the practice platform before exam day — the interface differs from a handheld calculator.
Pen and paper are provided at the test centre. Use them for intermediate working — do not try to calculate entirely in your head or on the calculator screen.
Part 1 is the most predictable part of the CRA. The question types are fixed. The calculator is allowed. Practice directly translates to improved performance. Start iatroX's adaptive GPhC calculations bank today.