Add a three-digit number to a three-digit number: step-by-step example
30 October 2026
Adding two three-digit numbers is an important skill for 11+ maths. When numbers get bigger, it's helpful to use written methods to keep your work neat and clear. This example will show your child exactly how to set out and solve a sum like this, step by step.
Worked example
346 + 287
Line up the numbers in columns: hundreds, tens and ones.
346 + 287
Start with the ones column: 6 + 7 = 13. Write 3 in the ones place. Carry over 1 to the tens column.
Move to the tens column: 4 + 8 = 12. Add the carried 1: 12 + 1 = 13. Write 3 in the tens place. Carry over 1 to the hundreds column.
Now the hundreds column: 3 + 2 = 5. Add the carried 1: 5 + 1 = 6.
The answer is 633.
Key insight: Always add from right to left and remember to carry over if the sum is 10 or more.
| Step | Calculation | Carry Over | Result Digit |
|---|---|---|---|
| Ones | 6 + 7 = 13 | 1 | 3 |
| Tens | 4 + 8 + 1 = 13 | 1 | 3 |
| Hundreds | 3 + 2 + 1 = 6 | 0 | 6 |
After working through this example, your child will see how to line up the digits and carry over when needed. They will recognise the pattern for adding each column, which helps with any similar question. Now, a similar three-digit addition is ready to practise next.
