Left-to-Right Subtraction (No Borrowing)
Level 2 Mental subtraction · Reviewed by The NumThink editorial team · Last reviewed
This page is part of the NumThink Mental subtraction course. Read why the method works, watch it run on worked examples, then drill it in the practice box below until it feels automatic.
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No signup · instant feedbackWhy it works
Just like left-to-right addition: the big parts move the total most, and you keep a clean running number in your head — 200, then 220, then 222.
When every top digit is at least as big as the bottom digit, there is no borrowing anywhere, making this the fastest possible route.
The steps
- Subtract the big parts. 845 − 623: 800 − 600 = 200.
- Then the middle parts. 40 − 20 = 20. Running total: 220.
- Finish small. 5 − 3 = 2. Total: 222.
Worked examples
Easy 58 − 23
Show the thinking
50 − 20 = 30
8 − 3 = 5
30 + 5 = 35.
Answer: 35
Medium 845 − 623
Show the thinking
800 − 600 = 200
40 − 20 = 20 → 220
5 − 3 = 2 → 222.
Answer: 222
Hard 9,431 − 5,215
Show the thinking
9,000 − 5,000 = 4,000
400 − 200 = 200 → 4,200
31 − 15 = 16 → 4,216.
Answer: 4,216
When to use it
- Digits that never force a borrow (top digits ≥ bottom digits) — the ideal case.
- A quick pass before choosing a method: if no borrows, take the straight road.
When NOT to use it
- Borrowing situations (52 − 38): counting up or near-round correction beats juggling negative digit gaps.
- Digits where some column tops are smaller — switch methods instead of forcing it.