Long Subtraction Calculator: Column Subtraction with Borrowing, Step by Step
Subtract whole or decimal numbers in columns with every borrowing (regrouping) step shown, including borrowing across zeros, plus the check by addition.
How it works
Line up by place value → subtract column by column from right to left → if the top digit is smaller than the bottom digit, borrow: take 1 from the next digit on the left (it drops by 1) and add 10 to the current top digit → across zeros, borrow from the first non-zero digit to the left; each 0 in between becomes 9 → check: difference + bottom number = top number
Long (column) subtraction takes one number from another by place value. Write the larger number on top with the ones (or the decimal points) lined up, then subtract each column starting from the right. When a top digit is smaller than the digit under it, you borrow (regroup): one ten from the column to the left becomes ten ones in this column, so the left digit goes down by 1 and the current digit goes up by 10. If the digit to the left is 0, keep moving left to the first non-zero digit, take 1 from it, and every 0 you passed becomes 9; this is the step most people find hardest, as in 5,003 − 1,867. Enter whole numbers or decimals with up to 15 digits before the point and 8 after; the arithmetic is exact, digit by digit. You get the difference, a place-value grid with the borrowed digits shown above the top number, a sentence for every column, the number of borrows and the check by addition. If the bottom number is the larger one, the calculator subtracts the other way and makes the answer negative. The long division calculator also uses repeated subtraction, but this page shows the subtraction method itself.
Worked example
Subtract 245 − 147. Ones column: 5 < 7, so borrow 1 from the tens: 4 becomes 3 and 5 becomes 15; 15 − 7 = 8. Tens column: 3 < 4, so borrow 1 from the hundreds: 2 becomes 1 and 3 becomes 13; 13 − 4 = 9. Hundreds column: 1 − 1 = 0. That gives 098, and dropping the leading zero the difference is 98, after 2 borrows. Check: 98 + 147 = 245.
Sources: CalculatorSoup: Long subtraction with regrouping calculator (245 − 147 example)
Frequently asked questions
How do you subtract with borrowing?
Work from the right. If the top digit is smaller than the bottom digit, cross out the digit to its left, write it 1 smaller, and put a 1 in front of the current digit (add 10). Now subtract that column and move on. For 52 − 17: 2 < 7, so 5 becomes 4 and 2 becomes 12; 12 − 7 = 5 and 4 − 1 = 3, giving 35.
How do you borrow across zeros?
Move left until you reach a non-zero digit, take 1 from it, and turn every 0 you passed into 9; the digit you started at gets 10 added. In 5,003 − 1,867 the 5 becomes 4, both zeros become 9 and the 3 becomes 13. Then 13 − 7 = 6, 9 − 6 = 3, 9 − 8 = 1 and 4 − 1 = 3, so the answer is 3,136.
Is borrowing the same as regrouping?
Yes. “Borrowing”, “regrouping”, “exchanging” and “trading” all describe turning 1 of a larger place value into 10 of the next smaller one. Regrouping is the term used in most US school standards; the result is the same.
How do you subtract decimals in columns?
Line up the decimal points, pad the shorter number with zeros so both have the same number of decimal places, subtract as with whole numbers and keep the point in the same place. For 52.07 − 8.9 write 52.07 − 08.90 = 43.17.
How do I check a subtraction answer?
Add the answer to the number you subtracted: you must get the top number back. For 245 − 147 = 98, check 98 + 147 = 245. The calculator shows this check under the result.
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This calculator is for educational purposes. Double-check important results before acting on them.