Teaching Subtraction with Regrouping (Borrowing): Step by Step

What Is Regrouping?

Regrouping (also called "borrowing") is what we do when we can't subtract a digit because the top number is smaller than the bottom number.

Example: 42 - 17

• We can't do 2 - 7
• We need to "borrow" from the tens place

Before Teaching Regrouping

Make sure your child understands:

• Place value (tens and ones)
• That 1 ten = 10 ones
• Basic subtraction facts

The Concrete Method (Base-10 Blocks)

Use blocks or draw pictures:

• Show 42 as 4 tens and 2 ones
• "Can we take away 7 ones? We only have 2."
• "Let's trade 1 ten for 10 ones"
• Now we have 3 tens and 12 ones
• Take away 7 ones → 5 ones left
• Take away 1 ten → 2 tens left
• Answer: 25

The Written Method

Step by step:

• Start with the ones place
• Ask: "Can I subtract?" (Is top ≥ bottom?)
• If no, regroup from the next column
• Cross out, reduce by 1, add 10 to current column
• Now subtract
• Move to the next column

Common Mistakes

Watch for these errors:

• Subtracting smaller from larger: 42 - 17 = 35 (taking 2 from 7)
• Forgetting to reduce: Borrowing but not crossing out the tens
• Borrowing when not needed: 45 - 23 doesn't need regrouping

Practice Tip

Start with problems that NEED regrouping in only one place:

• 32 - 15 (ones only)
• 70 - 40 (no regrouping needed — mix these in!)

Then progress to:

• 324 - 156 (two places)
• 400 - 123 (borrowing across zeros — hardest!)

The "Zero" Challenge

Subtracting across zeros is extra tricky:

Example: 300 - 156

• Can't borrow from 0 in the tens place
• Have to go to hundreds first
• 300 becomes 2 hundreds, 10 tens, 0 ones
• Then borrow again: 2 hundreds, 9 tens, 10 ones
• Now subtract: 10-6=4, 9-5=4, 2-1=1
• Answer: 144

Practice Resources

Try our subtraction practice:

• Grade 2 Subtraction
• Grade 3 Subtraction