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Subtraction with regrouping (borrowing): a parent’s guide

Regrouping is what most parents were taught to call borrowing: when the top digit in a column is smaller than the one under it, you trade 1 from the next column over for 10 in this one. Nothing is really borrowed and nothing is paid back. The number is just written a different way, so the subtraction can go column by column.

By The Kizupi team · Written · Updated

Key findings

  • Grade 2 children subtract within 1,000 and learn that “sometimes it is necessary to compose or decompose tens or hundreds” [1]. Decomposing a ten is regrouping.
  • Grade 2 also expects fluent subtraction within 100 using place-value strategies [1]. Fluent subtraction of multi-digit numbers with the standard algorithm comes in Grade 4 [2].
  • Regrouping never changes the number: 52 is 5 tens and 2 ones, or 4 tens and 12 ones. Only the way it is written changes.

What regrouping means

Take 52 − 27. In the ones column, 2 − 7 does not work with whole numbers. So trade one of the 5 tens for 10 ones: 52 becomes 4 tens and 12 ones. Now each column can be subtracted on its own.

With base-ten blocks or bundles of 10 straws, this is something a child can do with their hands: unbundle one ten into ten loose ones. Doing that a few times makes the crossed-out digits on paper make sense.

Example 1: 52 − 27

54212−2725
  • Ones: 2 is smaller than 7, so regroup. Cross out the 5 and write 4; the 2 becomes 12. 12 − 7 = 5.
  • Tens: 4 − 2 = 2.

So 52 − 27 = 25. Check by adding back: 25 + 27 = 52.

Example 2: regrouping twice, 642 − 385

65413212−385257
  • Ones: 2 is smaller than 5. Take 1 ten: 4 tens become 3 tens, and 2 ones become 12 ones. 12 − 5 = 7.
  • Tens: now 3 is smaller than 8. Take 1 hundred: 6 hundreds become 5 hundreds, and 3 tens become 13 tens. 13 − 8 = 5.
  • Hundreds: 5 − 3 = 2.

So 642 − 385 = 257. The tens digit changed twice (4, then 3, then 13), which is why it helps to cross out neatly and write each new digit small above.

Example 3: a zero in the middle, 403 − 168

4309313−168235

The ones need a ten, but there are 0 tens to take. So go to the hundreds first: 4 hundreds become 3 hundreds, and 0 tens become 10 tens. Now take 1 of those 10 tens: 10 tens become 9 tens, and 3 ones become 13 ones.

Then 13 − 8 = 5, 9 − 6 = 3 and 3 − 1 = 2, so 403 − 168 = 235. A quicker way to see it: 403 is 40 tens and 3 ones, so taking 1 ten leaves 39 tens and 13 ones.

The mistakes to look for

  • Subtracting the smaller digit from the bigger one. In 52 − 27, writing 7 − 2 = 5 in the ones column gives 35. If the answer plus the number taken away doesn’t give the top number, look for this first.
  • Forgetting to take 1 off the next column. The 12 gets written but the 5 stays a 5, giving 35 instead of 25.
  • Getting stuck at a zero. In 403 − 168, the tens have nothing to give. Go one more column to the left, as in Example 3.

How to help at home

  1. Ask before each column: “Is the top digit big enough?” If yes, subtract. If not, regroup first.
  2. Use the word your child’s class uses. Many schools say “regroup” or “trade” instead of “borrow”, because nothing is given back.
  3. Estimate first. 642 − 385 is about 600 − 400 = 200, so an answer like 343 means a column went wrong.
  4. Add back to check. The answer plus the number taken away gives the top number: 257 + 385 = 642.

If the crossed-out digits feel like magic, try the number bonds guide: seeing 12 as 10 and 2 is the idea regrouping is built on.

Questions parents ask

Is regrouping the same as borrowing?

Yes. It is the same method under a newer name. “Regrouping” says what happens: 1 ten is rewritten as 10 ones, and the number stays the same.

What grade learns subtraction with regrouping?

Grade 2: subtracting within 1,000, sometimes decomposing tens or hundreds [1]. The standard algorithm for bigger numbers is expected to be fluent in Grade 4 [2].

How do you subtract across a zero?

Regroup from the first column to the left that is not zero. In 403 − 168, the 4 hundreds become 3, the 0 tens become 10, then 9 after giving 1 ten to the ones, which become 13.

How do you check a subtraction answer?

Add the answer to the number you took away. You should get the top number: 235 + 168 = 403.

Keep going

Sources

  1. Common Core State Standards Initiative, Grade 2, Number and Operations in Base Ten (2.NBT.B.5, 2.NBT.B.7). Read November 11, 2026.
  2. Common Core State Standards Initiative, Grade 4, Number and Operations in Base Ten (4.NBT.B.4). Read November 11, 2026.

Cite this page: The Kizupi team, “Subtraction with regrouping (borrowing): a parent’s guide,” Kizupi, updated November 11, 2026, https://kizupi.com/guides/subtraction-with-regrouping.

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