About the Long Subtraction Calculator
Column subtraction is the written method for taking one number away from another, one place value at a time. When a top digit is smaller than the digit below it, you borrow 10 from the column to the left, which is also called regrouping or exchanging. This calculator lays the sum out in columns, marks each column that borrowed, and gives the difference. It lines decimals up on the point, and if the second number is bigger it takes the smaller from the larger and makes the answer negative, explaining why.
Updated October 2026
How to use the Long Subtraction Calculator
- 1Type the number you start with.
- 2Type the number to take away.
- 3Read the difference.
- 4Look at the working: a 1 on the top line marks a column that borrowed.
- 5Read the note under the working for the number of borrows.
A worked example with zeros
5,002 − 1,367: the ones column needs 2 − 7, so borrow. The tens and hundreds are 0, so borrow from the 5, which becomes 4; the hundreds and tens become 9, and the ones become 12. Then 12 − 7 = 5, 9 − 6 = 3, 9 − 3 = 6 and 4 − 1 = 3, giving 3,635. The tool shows three columns that borrowed.
Common mistakes
Most errors happen in the same few places.
- Subtracting the smaller digit from the larger in every column, whatever its position
- Forgetting to reduce the digit you borrowed from
- Treating zeros as if you could borrow from them directly
- Not lining up decimals on the point
Different names for the same idea
Borrowing, regrouping, exchanging and decomposition all describe the same step. Some countries teach the equal-additions method instead, adding ten to both numbers; it gives the same answer. This calculator shows the decomposition method used in most schools today.
Why it is worth practising
Column subtraction appears in everyday tasks such as working out change, budgets or the days between two dates. It also builds understanding of place value, which makes later topics like long division and algebra easier.
Checking by estimating
Before you subtract, round both numbers to estimate the answer: 5,002 − 1,367 is about 5,000 − 1,400 = 3,600. If your exact answer is far from the estimate, look again at the borrowing. Estimating first is a habit that catches most slips in exams.
Phone or computer
The working lines up in a fixed-width font and scrolls sideways for very long numbers. Borrowing is the part most people forget, so practise it on more sums. Try the Long Addition Calculator to check an answer, the Long Multiplication Calculator for the next skill, and the Percentage Change Calculator to see the difference as a percent.
Features
- Borrowing marked column by column
- Counts how many times you borrowed
- Decimals lined up on the point
- Negative answers explained
- Exact arithmetic for long numbers
- Copy the answer
Frequently asked questions
How do you borrow in subtraction?
If the top digit is smaller than the bottom one, take 1 from the digit to its left (making it one less) and add 10 to the top digit. Then subtract as normal.
What is regrouping?
Another name for borrowing. One ten is regrouped as ten ones, one hundred as ten tens, and so on.
How do you subtract across zeros?
Borrow from the first non-zero digit to the left; each zero in between becomes 9. In 5,002 − 1,367 the zeros become 9s after borrowing from the 5.
Can I subtract decimals?
Yes. The numbers are lined up on the decimal point and empty places are treated as zeros, so 12.5 − 0.75 = 11.75.
What if the second number is bigger?
Subtract the smaller from the larger and put a minus sign in front: 100 − 250 = −150.
How can I check my answer?
Add the answer to the number you took away. You should get the number you started with: 3,635 + 1,367 = 5,002.