Calculator Tips for Students
A calculator is most useful for checking work you have already done, not for replacing it. Used that way, it catches slips before your teacher does, shows you where a method went wrong, and helps you learn faster. Used the wrong way, it hides mistakes and leaves you stuck in tests where calculators are not allowed.
These eight calculator tips for students show how to check math homework properly, with examples of the mistakes calculators make easy to miss.
1. Work It Out First, Then Check
Solve the problem on paper first, with every step written down. Then use the calculator to check the answer.
If the two answers match, you can move on with confidence. If they do not, you have found a mistake while there is still time to fix it, and you know exactly which question to look at again. Typing the question straight into a calculator teaches you nothing, and it leaves you with no working to show, which is often where most of the marks are.
2. Estimate Before You Press Anything
Round the numbers and make a rough guess first. That way you will notice when a typing slip gives an answer that cannot be right.
Example: 48 × 19. Round to 50 × 20 = 1,000. The exact answer is 912, which is close to the estimate. If the calculator showed 91.2 or 9,120, you would know straight away that something was mistyped.
3. Use a Calculator That Shows Its Working
A plain answer only tells you whether you are right. A calculator that shows each step tells you where you went wrong, which is far more useful when learning a new method.
Example: 2/3 + 3/4. A common mistake is to add the tops and bottoms: 5/7. The fraction calculator shows the right method. It rewrites both fractions over the common denominator 12, giving 8/12 + 9/12 = 17/12, or 1 5/12. Comparing that step with your own working shows exactly which step to fix.
Every calculator on All Calculator shows its working in this way, so you can check the method as well as the answer.
4. Know How Your Calculator Handles Order of Operations
Calculators do not all follow the same rules.
- Scientific calculators and most online calculators follow the order of operations (PEMDAS or BODMAS). 6 + 4 × 3 = 6 + 12 = 18.
- Some basic calculators and phone calculators in simple mode work left to right as you type. They give (6 + 4) × 3 = 30, which is wrong.
If you are not sure how a calculator behaves, use brackets to make the order clear: 6 + (4 × 3).
Watch out for negative numbers too. On most scientific calculators, typing −3² gives −9, because the square is worked out before the minus sign. If you mean “negative three, squared”, type (−3)², which gives 9.
5. Check the Mode: Degrees or Radians
For trigonometry, a calculator in the wrong angle mode gives a completely different answer.
- sin(30) in degrees mode = 0.5
- sin(30) in radians mode ≈ −0.988
Most school questions use degrees. Look for a small “D” or “DEG” on the screen before you start. If your answers to every trig question are wrong, the mode is the first thing to check.
6. Round Only at the End
Rounding halfway through a calculation makes the final answer drift.
Example: a third of 300. Rounding 1/3 to 0.33 first gives 0.33 × 300 = 99. Keeping the full value gives 100.
Keep the full number on the calculator, or use the memory or answer button, and only round the final answer to the number of decimal places the question asks for.
7. Check the Answer Backwards
Undo the calculation to check it. This works for almost any question.
- Division: 912 ÷ 19 = 48. Check: 48 × 19 = 912.
- Percentages: 30% of 60 = 18. Check: 18 ÷ 60 = 0.30, which is 30%. The percentage calculator can do both directions.
- Square roots: √72 ≈ 8.485. Check: 8.485² ≈ 72. The square root calculator also gives the simplified form, 6√2, which many teachers ask for.
- Equations: put your answer back into the original equation and see if both sides match.
8. Ask Whether the Answer Makes Sense
Before you write an answer down, read the question again and ask whether it is realistic.
- A person cannot be 340 cm tall, so check your units.
- A percentage of marks cannot be more than 100%.
- A probability must be between 0 and 1.
- A car’s speed on a school trip is not 9,000 km/h.
Unit slips are the most common cause. If a question mixes centimetres and metres, or minutes and hours, convert everything to the same unit first.
Which Calculator to Use for Each Subject
| Subject | Calculator | What it helps you check |
| Percentages | Percentage calculator | Percent of a number, finding the whole |
| Test scores | Marks percentage calculator | Your score as a percentage |
| Increases and decreases | Percentage change calculator | Percentage increase and decrease questions |
| Fractions | Fraction calculator | Adding, subtracting, multiplying and dividing fractions |
| Decimals | Decimal to fraction calculator | Turning decimals, including repeating ones, into fractions |
| Roots and surds | Square root calculator | Square roots, cube roots and simplified radicals |
| Factors | Prime factorization calculator | Prime factors and factor trees |
| Physics | Velocity calculator | v = d/t and v = u + at questions |
| Computer science | Binary calculator | Binary addition, subtraction and bitwise logic |
For the formulas behind these topics, see our list of basic math formulas. For a step-by-step guide to the most common topic, read how to calculate percentage.
When Not to Use a Calculator
- When you are learning a new method. Do the first few questions by hand so the method sticks.
- When the paper is non-calculator. Many exams include papers or sections where calculators are not allowed, and others only allow approved models. Check your school’s or exam board’s rules well before the test.
- For simple sums. Practicing quick mental math, such as times tables and 10% of a number, makes you faster and helps you spot calculator slips.
Checking vs Copying
Using a calculator to check your own work is good study practice. Copying answers without understanding them is not, and it usually shows up in tests. Most teachers mark the working as well as the answer, so a correct number with no method can still lose marks. If your answer is wrong, use the calculator’s working to understand the mistake, then do the question again yourself.
Frequently Asked Questions
Is it OK to use a calculator for homework?
Usually, yes, unless your teacher says otherwise. The best approach is to do the work yourself first and use the calculator to check it. If a worksheet says “no calculator”, follow that instruction.
Why does my calculator give a different answer from my teacher’s?
The most common reasons are order of operations, degrees or radians mode, rounding too early, and how negative numbers are typed. Check those four things first.
What is the best calculator for checking math homework?
One that shows its working. Seeing each step lets you compare it with your own method and find the exact point where your answer went wrong.
Can a calculator be wrong?
The arithmetic is almost always right, but the answer can still be wrong if a number is mistyped, the wrong mode is set, or the calculator works through the sum in a different order than you meant. That is why estimating first and checking backwards matter.
Start Checking Your Work
Pick the topic you are working on and try the matching tool from the table above, or browse all math calculators and percentage calculators. Every one shows the full working, so you can check your method and your answer together.