Every year, thousands of students lose marks in GCSE Maths not because they do not understand the subject, but because of small, avoidable mistakes. These errors can happen under pressure in the exam hall, when nerves and time limits make it easy to miss details or rush through working.
The good news is that most of these mistakes are predictable, and once you know what they are, you can take simple steps to avoid them. In this blog, we highlight the ten most common errors students make in GCSE Maths and explain how to prevent them. By recognising these pitfalls now, you can save yourself unnecessary stress and secure the marks you deserve.
1. Not Showing Working
One of the most common reasons students lose marks in GCSE Maths is failing to show their working. Many questions award marks not just for the correct final answer but also for the method used to get there. These are called method marks, and they are designed to reward logical thinking even if the final step goes wrong.
For example, if a question requires solving a quadratic equation, setting it up correctly can already earn marks, even if a calculation slip later leads to the wrong answer. If no working is written down, the examiner has no choice but to award zero, even if the student understood part of the process.
The best habit is to write down every important step, even when it feels obvious. Laying out the method clearly not only secures extra marks but also makes it easier to check answers and spot small mistakes. In fact, examiners often comment that many students could achieve a higher grade simply by showing their full method consistently.
2. Misusing the Calculator
A calculator can be your best friend in the exam, but only if you know how to use it correctly. Many students lose marks not because they don’t understand the maths, but because they press the wrong buttons or rely on the calculator too much.
A common mistake is rounding too early. If you round an answer halfway through a calculation, the final result can be inaccurate. It is better to keep the full value in the calculator and only round at the very end. Another frequent slip is forgetting to check settings, such as whether the calculator is in degrees for trigonometry. Using the wrong mode can turn a correct method into the wrong answer instantly.
Some students also waste time by using the calculator for simple arithmetic they could do faster in their head, like adding 20 and 30. This over-reliance slows them down and increases the risk of typos.
The solution is to practise with your calculator well before the exam. Learn how to enter fractions, powers, and square roots, and make sure you are comfortable with brackets and memory functions. 👉 For more detailed advice, see our dedicated blog on How to Use Your Calculator Wisely in GCSE Maths.
3. Forgetting Key Formulas
GCSE Maths requires you to know and apply a wide range of formulas. Some are given on the exam paper, but many are not, and forgetting them can cost valuable marks. Common examples include Pythagoras’ theorem, trigonometric ratios, the quadratic formula, and the area and volume formulas for different shapes.
It is easy to assume that you will remember these in the heat of the exam, but pressure often makes even simple facts slip away. That is why memorisation must be part of your revision. A student who knows the formulas confidently can go straight to solving the problem, while someone who hesitates or guesses risks making mistakes.
A practical way to strengthen memory is to test yourself regularly. Write out formulas on flashcards, cover them up and try to recall them, or practise applying them in different contexts. Repetition builds confidence and ensures that the formulas come to mind quickly on exam day.
👉 On our site, you can download a complete GCSE Maths Formula Sheet and practise in the Formula Practice Room, where interactive exercises help you memorise everything you need.
4. Misreading the Question
Another very common mistake in GCSE Maths is misreading what the question is actually asking. Under exam pressure, it is easy to rush through the words and miss key instructions such as “estimate,” “simplify,” “give your answer to two decimal places,” or “show that.”
Even if the calculations are correct, failing to follow the instruction means the answer will not earn full marks. For example, a student might correctly calculate a probability but leave it as a decimal when the question asked for a fraction. Or they might give an exact value when the examiner specifically asked for a rounded estimate.
The best way to avoid this mistake is to slow down when reading the question. Underline important words and check them again before writing your final answer. Always ask yourself, “What is the examiner really looking for here?” A few extra seconds spent double-checking the wording can save valuable marks.
5. Weakness with Fractions, Decimals, and Percentages
Fractions, decimals, and percentages form the foundation of GCSE Maths, yet they are also one of the most common problem areas for students. Many questions across the papers depend on these skills, either directly or hidden within more complex problems. For example, an algebra question might still require adding fractions correctly, or a geometry task might involve converting a decimal into a percentage.
Students often make mistakes when converting between these forms, simplifying fractions, or applying percentage increases and decreases. Even a small slip can lead to the wrong final answer and a loss of marks.
The key to improving is regular practice with the basics. Start with simple tasks, such as writing decimals as fractions, then move on to multi-step problems like percentage change or compound interest. Building fluency in these skills makes the harder questions much more manageable.
👉 Our quizzes are designed to give repeated practice with fractions, decimals, and percentages until these essential skills feel natural. Mastering them is one of the quickest ways to boost your overall GCSE Maths grade.
6. Mixing Up Negative Numbers and BIDMAS
Questions involving negative numbers and the order of operations (BIDMAS) regularly catch students out. Even strong candidates can slip up when a minus sign is involved or when they forget which operation comes first.
A typical mistake is treating subtraction and negative numbers as the same thing. For example, students sometimes confuse “–3 × –4” with “–3 – 4,” leading to the wrong result. Another common error is breaking the rules of BIDMAS by adding before multiplying, or ignoring brackets altogether.
These errors are frustrating because the methods are not difficult, yet under time pressure it is easy to overlook them. The solution is practice and careful checking. Write each step clearly, include brackets when needed, and slow down when negatives appear. Even a quick estimation can help: if the answer should be positive, spotting a negative result is a clear sign to check again.
👉 We include plenty of practice questions on BIDMAS and negative numbers in our quizzes. By working through these repeatedly, students can train themselves to avoid these simple but costly mistakes.
7. Struggling with Word Problems
Word problems often feel more intimidating than straightforward calculations because they hide the maths inside a written scenario. Many students know the methods but lose confidence when faced with a question that looks like a story rather than a clear instruction.
The most common mistake is trying to jump straight into calculations without fully understanding what the question is asking. Important details are sometimes skipped, or the wrong numbers are used, leading to errors even when the maths itself is correct.
A better approach is to slow down and break the problem into steps. First, read carefully and highlight the key information. Next, identify exactly what needs to be found — is it a total, a difference, a probability, or an unknown value? Then translate the words into maths by writing down equations or expressions before you start calculating. Finally, check whether the answer makes sense in the context of the problem.
👉 We have a dedicated blog on How to Master Word Problems in GCSE Maths where you can learn detailed strategies and practise with examples. With the right method, word problems stop being scary and become a chance to show real understanding.
8. Poor Time Management in the Exam
Time management is one of the biggest challenges in GCSE Maths. Many students spend far too long on a single question, especially one that looks difficult, and then run out of time before reaching the later parts of the paper. This can mean losing marks on questions they would have been able to answer correctly.
A good rule of thumb is to allow roughly one minute per mark. For example, if a question is worth five marks, plan to spend no more than about five minutes on it before moving on. If you find yourself stuck, make a note, leave some working, and return later if time allows. It is better to collect easy marks across the whole paper than to spend too long chasing one tricky answer.
It is also important to practise this skill before the exam. Working through full past papers under timed conditions helps you get used to the pace and reduces stress on the day. The more you practise, the more natural it becomes to move steadily through the paper without panicking about the clock.
👉 On our site, you can practise timed quizzes and mock exams that simulate real exam conditions. This builds the stamina and confidence needed to stay on track from the first question to the last.
9. Leaving Out Units or Labels
A surprisingly common mistake in GCSE Maths is forgetting to include the correct units or labels in the final answer. Even if the calculation is perfect, missing the units can cost marks. For example, giving an answer of “12” instead of “12 cm²” in an area question, or writing “0.6” for a probability without clarifying whether it is a fraction, decimal, or percentage.
Examiners expect answers to be fully clear and unambiguous. Units such as centimetres, kilograms, or pounds show exactly what the number represents. In statistics questions, labels on axes or answers written as “mean = 7.2” rather than just “7.2” demonstrate precision.
The easiest way to avoid this mistake is to develop a habit of checking the question wording carefully. If the question asks for the answer “to the nearest degree” or “in kilograms,” then that exact form must appear in the solution. Before moving on, always double-check whether a unit, label, or rounding instruction has been included.
👉 Our practice resources highlight these details so that you get used to writing complete answers, not just numbers. Making this a habit now will stop you from losing easy marks in the real exam.
10. Not Checking Answers
Many students hand in their exam paper without taking the time to check their work. This is one of the easiest ways to lose marks because small slips in arithmetic, rounding, or copying numbers can turn a correct method into the wrong final answer.
Checking does not have to take long. A quick estimate can tell you whether the answer makes sense. For example, if you divide 200 by 5 and your calculator shows 80, you should instantly notice that the answer is too high. Similarly, re-reading a word problem can reveal if the units or format of your answer match what was asked.
Even in the last few minutes of the exam, looking back through your paper can gain valuable marks. Correcting just one or two careless mistakes could make the difference between a grade 4 and a grade 5, or between a 6 and a 7.
👉 When you practise with our quizzes and past papers, make it a routine to check every answer before moving on. Building this habit early means it will feel natural in the real exam, giving you the best chance to secure every mark you deserve.
Conclusion
Mistakes in GCSE Maths are not a sign of weakness. They are often just the result of rushing, misreading, or overlooking small details. By slowing down, showing clear working, managing your time wisely, and checking your answers, you can avoid the traps that cost so many students valuable marks.
The key is to practise regularly and build good habits before exam day. Use our quizzes, past papers, and practice rooms to strengthen your weak areas and train yourself to spot errors early. Every mark matters, and avoiding these common mistakes could be the difference between one grade and the next.
With awareness and preparation, you can turn mistakes into opportunities for improvement and walk into your GCSE Maths exam with confidence.