Three-Digit Subtraction With Regrouping, Step by Step
Quick answer
To teach 3-digit subtraction with regrouping, have your child start with the ones column on the right and work left. When the top digit is smaller than the bottom digit, borrow 1 from the next column, which adds 10 to the current column. Cross out the digit you borrowed from and write the new smaller number above it. Then subtract and move to the next column. Most kids learn this in 2nd and 3rd grade.
Three-digit subtraction with regrouping is where subtraction stops being a quick mental trick and becomes a step-by-step routine. The good news is that the routine is the same every time, and once your child learns it, they can subtract any pair of numbers. Below is how to walk through it, what to do when zeros get in the way, and the mistakes to watch for.
What is 3-digit subtraction with regrouping?
Three-digit subtraction means subtracting numbers like 432 - 158, where each number has a hundreds place, a tens place, and a ones place. Regrouping (also called borrowing) is what you do when a digit on top is smaller than the digit below it. You borrow from the next column to the left, which adds 10 to the column you’re working in.
This skill shows up in 2nd and 3rd grade:
- 2nd grade (2.NBT.B.7): add and subtract within 1,000 using place-value strategies, including regrouping.
- 3rd grade (3.NBT.A.2): fluently add and subtract within 1,000 using the standard algorithm.
Kids are usually ready for this once they can subtract two-digit numbers with regrouping and understand that a number like 432 means “4 hundreds, 3 tens, and 2 ones.”
How to subtract 3-digit numbers with regrouping, step by step
Let’s work through 432 - 158.
Step 1: Stack the numbers and line up the places
Write the numbers vertically so hundreds line up over hundreds, tens over tens, and ones over ones.
432
- 158
-----Step 2: Start with the ones column
Look at the ones: 2 minus 8. You can’t take 8 from 2, so you need to borrow.
Step 3: Borrow from the tens column
The tens column has a 3. Borrow 1 ten from it, which leaves 2 tens. That 1 ten you borrowed becomes 10 ones, so the 2 in the ones column becomes 12.
Cross out the 3 and write 2 above it. Cross out the 2 and write 12 above it.
4 ²3 ¹²
- 158
-----Now subtract the ones: 12 minus 8 = 4. Write 4 in the ones place.
Step 4: Move to the tens column
Now you have 2 tens minus 5 tens. You can’t do that, so borrow from the hundreds.
The hundreds column has a 4. Borrow 1 hundred, which leaves 3 hundreds. That 1 hundred becomes 10 tens, so the 2 in the tens column becomes 12 tens.
Cross out the 4 and write 3 above it. Cross out the 2 and write 12 above it.
³4 ¹²3 ¹²
- 158
-----
4Subtract the tens: 12 minus 5 = 7. Write 7 in the tens place.
Step 5: Subtract the hundreds column
Now you have 3 hundreds minus 1 hundred = 2. Write 2 in the hundreds place.
³4 ¹²3 ¹²
- 158
-----
274Answer: 274.
How to handle borrowing across zeros
Borrowing across zeros is the step that makes kids (and parents) want to quit, but it follows the same rule: keep moving left until you find a digit you can borrow from, then pass it back through each zero.
Take 500 - 237.
- Ones column: 0 minus 7. You can’t do that, so borrow from the tens. But the tens column is also 0.
- Keep moving left: The hundreds column has a 5. Borrow 1 hundred from it, leaving 4 hundreds. That 1 hundred becomes 10 tens.
- Pass it back: Now the tens column has 10. Borrow 1 ten from it, leaving 9 tens. That 1 ten becomes 10 ones.
- Now subtract: 10 minus 7 = 3 (ones), 9 minus 3 = 6 (tens), 4 minus 2 = 2 (hundreds).
Answer: 263.
The crossed-out version looks like this:
⁴5 ⁹0 ¹⁰0
- 237
-----
263It looks messy on paper, but the logic is always the same: borrow, pass it back, then subtract.
The 4 mistakes kids make most (and how to fix them)
Ways to practice 3-digit subtraction at home
Practice sticks when it’s short, real, and varied. A few ideas:
- Odometer math: subtract the miles at the start of a trip from the miles at the end.
- Scorekeeping: subtract points lost from a starting total in a game.
- Pages left: subtract the current page number from the total pages in a book.
- Daily 5: five problems a day, mixing ones that need one borrow and ones that need two or have zeros.
Keep sessions to five or ten minutes. When your child gets one wrong, point to the column where the mistake happened and let them try again before you show the answer. That second try is where the learning happens.
How to check the answer (and teach your child to check theirs)
The simplest check is addition. Add the answer to the number you subtracted. If you get the number you started with, the subtraction is correct.
For 432 - 158 = 274, check by doing 274 + 158. If it equals 432, you’re right.
Teach your child this check and have them use it on the last problem of every practice session. Catching their own mistakes builds confidence and makes them careful.
How to know your child is ready to move on
Your child has mastered 3-digit subtraction with regrouping when they can:
- Subtract two 3-digit numbers that need regrouping in one or two columns.
- Borrow correctly across zeros.
- Explain why they borrow (“I can’t take 8 from 2, so I borrow 1 ten and that makes it 12”).
- Check their answer by adding.
- Solve simple word problems that use 3-digit subtraction.
When those feel solid, the natural next steps are 4-digit subtraction (same routine, one more column) and multi-step word problems that mix addition and subtraction.
Free Three-digit Subtraction With Regrouping Worksheet
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The easiest way to give your child practice
For most parents, the hardest part of teaching 3-digit subtraction with regrouping isn’t the math. It’s coming up with enough of the right problems and keeping your child willing to do them. That’s where Octolearn helps: describe the skill (“3-digit subtraction with regrouping”), and it builds a grade-matched practice set with read-aloud support, a hint and a second try on every question, and stars that keep kids coming back.