Part 1 is 40 calculations in 120 minutes, three minutes each, with a typed numerical answer and no options. It is a separate pass requirement. The framework says each assessment includes at least one question on each of twelve topics. Most lost marks come from units, a missed step or ignoring a rounding instruction. Use a fixed routine: read, list the data, convert units, calculate, round as instructed, then check the size and the units of the answer.
Why Part 1 is its own problem
Part 1 is not a harder version of Part 2. It is a different task. In Part 2 you can eliminate options and work backwards. In Part 1 you type the answer, so a single slip in a conversion produces a confident wrong number. And because Part 1 must be passed on its own, strong clinical knowledge cannot compensate.
The good news is that Part 1 is the most trainable part of the assessment. Calculations have methods, methods have habits, and habits improve with short daily practice. Our study plan builds this in.
Our practice bank writes calculations as five-option single best answer items so they can be marked automatically. The wrong options are built from common errors, which makes them good for learning the traps. They do not reproduce the typed-answer experience, so also practise without options. Cover the choices, work out the answer, then look.
The routine for every problem
- Read the last line first. Find out what is wanted and in what unit: a dose in mg, a volume in mL, a rate in mL/hour, a quantity of tablets.
- List the data. Pull the numbers and units out of the stem. Note any formula provided. Mark any rounding instruction.
- Convert to compatible units. Do this before the main calculation, not during it.
- Choose the method and write the line. Write the working with units on each line. If you cannot name the method, move on and come back.
- Calculate with the calculator, not in your head. Re-enter the numbers rather than trusting memory.
- Round as instructed. If no instruction is given, think about what is practically measurable.
- Sense-check. Is the size plausible? Is it more than the adult dose? Could you measure it with the device in the question?
The twelve topics and how to approach each
Doses and dose regimens
Distinguish the dose from the daily dose, and a per-day figure from a per-dose figure. Many errors come from dividing by the number of doses twice, or not at all. For weight-based doses, use the weight given in the question, in kilograms.
Dosage and unit conversions
Know the ladder: 1 g is 1,000 mg, 1 mg is 1,000 micrograms, and 1 microgram is 1,000 nanograms. Write microgram and nanogram in full, as the BNF does. Convert before calculating, and say the conversion aloud in your head.
Estimation of kidney function
The stem usually supplies the formula or the values. Recall that the Cockcroft-Gault method uses age, weight, sex and serum creatinine in micromol/L to estimate creatinine clearance in mL/min. If the formula is not provided, confirm it from the BNF while you revise and learn the two constants for men and women. Then apply the result to a dose band in the question.
Displacement volumes and values
When a powder is reconstituted, it adds volume. The displacement volume changes the concentration you end up with, so subtract it from the diluent volume if the stem asks for a final volume. Suppository questions use the displacement value, the amount of drug that displaces one gram of base.
Concentrations
Percentage w/v means grams in 100 mL. A 1 in 1,000 solution is 1 g in 1,000 mL, or 1 mg/mL. Convert between percentages, ratios and mg/mL in one pass, and check the answer against a known product.
Dilutions
The relation C1V1 = C2V2 covers many questions. For mixing two strengths, use alligation or simple proportion. State which volume is the final volume before you start.
Molecular weight and millimoles
Moles equal mass divided by molecular weight. Millimoles equal milligrams divided by molecular weight. Take care with salts, where the stem may specify the weight of the whole salt or of the ion.
Using formulae provided
The formula is given, so the skill is substitution and units. Write the formula, substitute with units, then calculate. Do not simplify mentally.
Infusion rates
Work from the dose to the volume to the rate. Typical rates are in mL/hour, with drops per minute for gravity sets, mg/hour or units/hour. Confirm the concentration of the bag or syringe, and the time over which the dose must run.
Pharmacokinetics
Expect half-life, steady state, loading dose and clearance in simple forms. Remember that steady state is reached after about four to five half-lives. Most questions give you the equation, so practise reading it.
Health economics
These are small arithmetic problems on cost per quality-adjusted life year, number needed to treat or a cost comparison. Take the difference in costs and the difference in outcomes before dividing.
Quantities to supply
Convert the dose, frequency and duration into a total quantity, then into packs. Check whether the question wants the exact quantity or the number of whole packs, and for controlled drugs remember the quantity is written in words and figures.
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Four worked examples (original, with the method shown)
These are invented for practice. They show how to lay out working, with units on every line, and they are not recalled from any paper.
Example 1: a weight-based liquid dose
A child weighs 14 kg. The prescribed dose is 15 mg/kg per dose. The suspension contains 250 mg in 5 mL. What volume is one dose? Dose = 14 kg x 15 mg/kg = 210 mg. Concentration = 250 mg / 5 mL = 50 mg/mL. Volume = 210 mg / 50 mg/mL = 4.2 mL. Sense-check: a bit under the 5 mL that contains 250 mg, which matches a dose of 210 mg.
Example 2: an infusion rate
A dose of 750 mg in 100 mL of infusion fluid must run over 30 minutes. What is the rate in mL/hour? The volume is 100 mL and the time is 0.5 hour. Rate = 100 mL / 0.5 hour = 200 mL/hour. If the stem had asked for mg/hour, you would calculate 750 mg / 0.5 hour = 1,500 mg/hour. The question decides the unit.
Example 3: a kidney function estimate with the formula supplied
A man aged 70 years weighs 80 kg and has a serum creatinine of 110 micromol/L. The formula given is (140 minus age) x weight x 1.23, divided by serum creatinine, for a result in mL/min. Step one: 140 minus 70 = 70. Step two: 70 x 80 = 5,600. Step three: 5,600 x 1.23 = 6,888. Step four: 6,888 / 110 = 62.6 mL/min. Round only at the end, and only as instructed.
Example 4: concentrations
How many mg/mL is a 0.5% w/v solution? 0.5% w/v is 0.5 g in 100 mL, which is 500 mg in 100 mL, which is 5 mg/mL. How many mg/mL is a 1 in 1,000 solution? 1 g in 1,000 mL is 1,000 mg in 1,000 mL, which is 1 mg/mL. Learn these two conversions until they are automatic.
The traps the framework hints at
- Rounding instructions. GPhC feedback has pointed out that candidates often miss them. Underline the instruction in your working.
- Multi-step problems. A dose, then a volume, then a rate. Write each step on its own line with its unit.
- Practical measurement. If the stem asks what can practically be measured, an answer with more decimal places than the device allows is not the best answer. Read the syringe size and its graduations.
- Per kilogram or per square metre. Body-surface-area dosing needs a formula, usually supplied. Height and weight units matter.
- Unit-based drugs. Insulin and heparin are in units. Do not convert units to milligrams.
A weekly drill that works
Practise 20 to 30 minutes most days, using the rotation in the study plan. Once a week, do ten problems timed at three minutes each, with no options and a typed answer. After each session, record the cause of every miss in the error log: conversion, method, arithmetic, rounding or misread. After two weeks, the log will show a dominant cause, and that cause is the fix to make.
Check the answer against the size you expect before you type. If a calculation tells you to give a baby 5 g of paracetamol, the arithmetic is irrelevant. Stop and recheck the conversion.
The calculator
You may use an approved physical calculator or the on-screen one in both parts, although the on-screen calculator appears only on Part 2 questions that need one. The approved list in the 2026 specification includes Aurora DT210 and HC133, Casio HS-8VA, MX-8B and MX-8S models, Casio SL-300SV and Catiga CD-8185. Practise with the model you will bring. Know how it handles brackets, memory and decimal places, because a habit of re-keying numbers beats a clever shortcut.
Check the permitted-items list for your sitting. A calculator that was allowed last year may not be allowed this year, and a calculator that is not on the list will be taken from you.
Time
Three minutes per question is generous for a simple conversion and tight for an infusion problem with a unit change. Bank time on easy items, flag a hard one after about four minutes, and return to it. Every item is worth the same single mark. If you finish early, re-do two or three problems from scratch with a different method and compare the answers.
Sit a timed GPhC Registration Assessment mock exam
Blueprint-weighted questions under exam timing, then a breakdown of your result by domain.
For the topic list as a whole, see high-yield topics, and for the domain summary see the pharmaceutical calculations page.
Frequently asked questions
How many calculation questions are in the GPhC exam?
Part 1 has 40 calculations with typed numerical answers, to be completed in 120 minutes. That is three minutes a question.
Do I get options in Part 1?
No. You type a number. Our practice bank uses five-option single best answer items for calculations, so also practise by covering the options and typing your own answer.
Can I use a calculator in Part 1?
Yes. You may use an approved physical calculator from the GPhC list or the on-screen calculator. Check the permitted-items list for your sitting.
Are rounding rules tested?
Yes. GPhC feedback has said candidates often miss rounding instructions in the question. Follow the stem exactly, and think about what is practically measurable if no instruction is given.
What calculation topics will appear?
The framework says each assessment includes at least one question on each of twelve topics: doses and regimens, unit conversions, kidney function, displacement, concentrations, dilutions, molecular weight, provided formulae, infusion rates, pharmacokinetics, health economics and quantities to supply.