# How to help your child with column subtraction Source: https://askthena.com/blog/column-subtraction-how-to-help-your-child Published 30 October 2026. For parents in the UK. Column subtraction is a written method where you line two numbers up by place value (ones under ones, tens under tens) and subtract one column at a time, starting with the ones on the right. When the top digit in a column is smaller than the one underneath, your child **exchanges** one from the column to the left. Many parents were taught to call this borrowing. Most children in England learn the formal written method in Year 3 and keep using it, with bigger numbers, right through Key Stage 2. ## Which year group learns what The National Curriculum for England builds up to it gradually: - **Year 1 and Year 2:** subtracting with objects, number lines and mental methods, and learning that 34 is three tens and four ones. Many schools start showing the column layout with blocks in Year 2. - **Year 3:** formal written column subtraction with numbers up to three digits. - **Year 4:** numbers up to four digits. - **Year 5 and Year 6:** numbers with more than four digits, then decimals, money, measures and problems with more than one step. So if your Year 2 child is still drawing sticks and dots, that is exactly where they should be. The written method only works once a child really understands tens and ones. ## How schools teach it, step by step Most primary schools use an approach called concrete, pictorial, abstract. Children handle real objects first, then draw them, and only then move to digits on their own. Here is how that looks with 73 − 28. ### Step 1: real objects Children use base 10 blocks (sometimes called Dienes): long sticks for tens and small cubes for ones. Some schools use place value counters instead. Your child builds 73 as seven ten sticks and three cubes. They need to take away 8 ones but only have 3. So they swap one ten stick for ten single cubes. Now they have six tens and thirteen ones, and they can take away two tens and eight ones, leaving four tens and five ones: 45. That swap is the heart of the whole method. Your child sees that the number hasn't changed. It is still 73, just arranged differently. ### Step 2: drawing it Next, children draw lines for tens and dots for ones. They cross out one line and draw ten dots in its place, then cross out what they are taking away. ### Step 3: the expanded method Many schools then split the numbers up so the place value stays visible: ``` 70 + 3 - 20 + 8 ``` Your child crosses out the 70 and writes 60 above it, then turns the 3 into 13. Now 13 − 8 = 5 and 60 − 20 = 40, so the answer is 40 + 5 = 45. ### Step 4: the compact method Finally, the numbers are written the short way: ``` 6 13 7 3 - 2 8 ------ 4 5 ``` The 7 is crossed out and a small 6 written above it. A small 1 goes in front of the 3 to make 13. Then 13 − 8 = 5 in the ones column and 6 − 2 = 4 in the tens column. Schools also teach children to check by adding: 45 + 28 = 73, so the answer is right. ## The words your child's teacher uses The vocabulary has changed since many of us were at school, and using the same words as the teacher really helps. - **Ones**, not units. - **Exchange**, not borrow. Borrowing suggests you pay something back, and you never do. Exchanging means swapping one ten for ten ones of exactly the same value. - **Place value**, **digit** and **column**. - **Difference**, as in "find the difference between 73 and 28". Some parents learned a different method at school, sometimes called equal addition, where you add ten to the top digit and one ten to the bottom number. It works, but mixing two methods can muddle a child who is just getting confident. Ask your child to show you how they do it in class, and follow their lead. Many schools will also share their calculation policy if you ask. ## Zeros: the bit most children find hardest Sums like 403 − 168 trip up lots of children, because there are no tens to exchange from. Your child has to go one column further. ``` 3 9 13 4 0 3 - 1 6 8 --------- 2 3 5 ``` Here is what happens: 1. In the ones, 3 − 8 won't work, and there are no tens to swap. 2. So exchange one hundred for ten tens. The 4 becomes 3 and the 0 becomes 10. 3. Now exchange one of those tens for ten ones. The 10 becomes 9 and the 3 becomes 13. 4. Subtract: 13 − 8 = 5, then 9 − 6 = 3, then 3 − 1 = 2. The answer is 235. Check: 235 + 168 = 403. Good [practice sums with zeros](https://askthena.com/uk/worksheets/subtraction) are 302 − 145 (157), 500 − 236 (264) and 1000 − 357 (643). ## Four common mistakes and how to fix them These come up in almost every class. None of them mean your child is bad at maths. They usually mean one step hasn't quite clicked yet. ### Taking the smaller digit from the bigger one For 52 − 27, your child does 7 − 2 = 5 in the ones and writes 35. They have subtracted the smaller digit from the bigger one instead of exchanging. Checking by adding shows it: 35 + 27 = 62, not 52. The correct answer is 25. ### Forgetting to change the next column Your child turns the 3 into 13 but leaves the 7 as it is, so 73 − 28 becomes 55. Ask, "Where did that extra ten come from?" ### Lining up wrongly For 145 − 32, the 32 ends up under the 14 instead of the 45. Squared paper, one digit per square, fixes this quickly. ### Exchanging when there's no need Some children exchange in every column, even for 87 − 34. Ask them to look at each column first: is the top digit big enough? ## Five quick games for the kitchen table Ten minutes a few times a week does more than an hour on Sunday. - **Coin swaps.** Make 73p with seven 10p coins and three 1p coins. Ask your child to give you 28p. They will need to swap a 10p for ten 1p coins, which is exchanging in real life. For zeros, start with four £1 coins and three 1p coins and ask for £1.68. - **Estimate first.** Before working out 73 − 28, ask, "About how much will it be?" Something like 70 − 30 = 40 is close enough. If the answer comes out at 101, they will spot that something has gone wrong. - **Spot my mistake.** Write a sum with a deliberate error, such as 64 − 39 = 35, and ask your child to find it. Children love catching a grown-up out, and explaining the mistake shows real understanding. (The answer is 25.) - **Shopping change.** "If something costs 37p and I pay with £1, how much change?" That is 100 − 37, which needs exchanging across a zero. - **Would you use a column?** Give a mix: 1000 − 999, 80 − 30 and 724 − 389. Schools want children to choose. The first two are quicker in their head, and the last one is a good job for the column method. ## Questions to ask when your child gets stuck Try asking rather than telling. These questions work well: - "Which column do we start with?" - "Is the top digit big enough to take the bottom one away?" - "What could we swap?" - "Has the number changed, or just how it's arranged?" - "How could you check your answer?" If your child is upset, stop and go back to coins or blocks. That is exactly what teachers do when a method wobbles. If your child keeps getting stuck over several weeks, have a quick word with the class teacher. Ask which method and words the class uses, and whether there is anything they would like you to practise at home. ## A simple plan for this week Ask your child to teach you one column subtraction the way they do it at school. Then do three sums together, including one with a zero, and check each answer by adding. Keep coins handy so you can show an exchange whenever the written method gets confusing. If you'd like some extra help, [Thena teaches column subtraction](https://askthena.com/blog/meet-thena) the way UK schools do, writing each step on her board column by column. If exchanging across zeros is tricky for your child, she remembers and brings it back in later lessons. The first 3 lessons are free, with no card needed. ## Questions parents ask ### What year do children learn column subtraction? In England, the National Curriculum introduces formal written column subtraction in Year 3, with numbers up to three digits. Children move on to four-digit numbers in Year 4 and bigger numbers, decimals and money in Years 5 and 6. Many schools show the column layout with blocks earlier, in Year 2. ### Why do schools say exchanging instead of borrowing? Borrowing suggests you will pay something back, which you never do. Exchanging describes what really happens: you swap one ten for ten ones, so the number keeps the same value and is just arranged differently. ### Should I teach my child the method I learned at school? It is best to use the method your child's school uses, even if yours gives the right answer. Ask your child to show you how they do it in class, or ask the teacher for a copy of the school's calculation policy. ### Why does my child get column subtraction wrong when there is a zero? Subtracting across a zero is the hardest part, because your child has to exchange twice: from the hundreds into the tens, then from the tens into the ones. Practising with coins, swapping a £1 coin for ten 10p coins, helps them see what is happening. ### Should my child use column subtraction for every sum? No. Schools want children to choose sensibly, so sums like 1000 − 999 or 80 − 30 are quicker in their head. Column subtraction is most useful when the numbers are bigger and need exchanging, such as 724 − 389.