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Subtracting Right to Left

Grades 1–3 Subtraction The schoolbook method

The standard subtraction method starts at the ones column and moves left. When the top digit of a column is smaller than the bottom digit, you borrow — take one from the next column over (that's worth ten in this one).

Why it works

Borrowing is just place value being honest: one ten is ten ones, one hundred is ten tens. When a column can't pay, the column to its left lends it a bundle of ten. The total on top never changes — it's just re-bundled.

Worked example: 524 − 276

4 11 ← the 2 became 11 after borrowing; 52̶ 4 the 5 became 4 − 2 7 6 = 2 4 8
  1. Ones: 4 − 6 can't go. Borrow 1 ten from the tens column: the 2 becomes 1, and the 4 becomes 14. 14 − 6 = 8.
  2. Tens: now the tens column shows 1 (not 2). 1 − 7 can't go. Borrow 1 hundred from the hundreds: the 5 becomes 4, and the 1 becomes 11. 11 − 7 = 4.
  3. Hundreds: 4 − 2 = 2.
  4. Answer: 248. Check: 248 + 276 = 524. ✓
The golden rule A borrow always turns the borrowed-from digit down by one and turns the needy digit up by ten. Cross out the old digits and write the new ones above them — tiny, so they don't get confused with the problem.

Borrowing across a zero

Zeros make borrowing look scary but it's just a chain of borrows:

2 9 9 3̶0̶0̶ − 1 2 5 = 1 7 5

300 − 125: the ones need to borrow, but the tens has nothing — so the tens borrows from the hundreds first (300 → 2 hundreds + 10 tens), then the ones borrows from the tens (10 tens → 9 tens + 10 ones). Now: 10 − 5 = 5, 9 − 2 = 7, 2 − 1 = 1 → 175.

Try it yourself:
  1. 83 − 47  (answer: 36)
  2. 652 − 278  (answer: 374)
  3. 1,000 − 456  (answer: 544)

The other direction: you can also subtract by starting with the biggest piece — see the left-to-right method.

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