Long Addition Calculator: Column Addition with Carrying, Step by Step
Add up to 20 whole or decimal numbers in columns and see every step: digits lined up by place value, each column sum, the carries and the final answer.
How it works
Line up the numbers by place value → add each column from right to left: column total = digits in the column + carry from the column to its right → write total mod 10 → carry ⌊total ÷ 10⌋ to the next column on the left → when the last column is done, write any remaining carry in front
Long (column) addition adds several numbers by place value. Write them under one another so the ones line up (or, with decimals, so the decimal points line up, padding the shorter decimals with zeros). Then add one column at a time, starting at the right. If a column adds up to 10 or more, write only its last digit and carry the tens part to the next column on the left, where it is added in with that column’s digits. When the leftmost column is done, any carry is written in front of the answer. Type up to 20 numbers, one per line or separated by + signs; each may have up to 15 digits and 8 decimal places, and the arithmetic is exact digit by digit with no rounding. You get the sum, a place-value grid with the carries on top that looks like the written method, and a sentence for every column. This page is only for addition; the long multiplication and long division calculators show the other written methods, and the long subtraction calculator shows borrowing.
Worked example
Add 937 + 129 + 248. Ones column: 7 + 9 + 8 = 24, write 4 and carry 2 to the tens. Tens column: 2 (carried) + 3 + 2 + 4 = 11, write 1 and carry 1 to the hundreds. Hundreds column: 1 (carried) + 9 + 1 + 2 = 13, write 3 and carry 1 to the thousands. Thousands column: 1 (carried) = 1, write 1. The sum is 1,314, with 3 carries over 4 columns.
Sources: CalculatorSoup: Long addition calculator (937 + 129 + 248 and decimal examples)
Frequently asked questions
How do you do long addition step by step?
Stack the numbers so digits of the same place value are in one column. Add the ones column first. Write the ones digit of that column total under the line and carry the tens digit to the top of the next column. Repeat for the tens, hundreds and so on, adding any carried digit, and write the last carry in front of the answer.
What does carrying mean in addition?
Carrying (also called regrouping) moves a group of ten from one column to the next. If the ones column adds up to 24, that is 2 tens and 4 ones: write 4 in the ones place and add the 2 tens to the tens column.
How do you add decimals with long addition?
Line up the decimal points, not the last digits. Pad the shorter decimals with zeros so every number has the same number of decimal places, add as with whole numbers and put the point in the answer under the other points. For 37.5 + 129.44 + 48.123, add 37.500 + 129.440 + 48.123 = 215.063.
Can a carry be more than 1?
Yes, when you add three or more numbers. Nine numbers ending in 9 give 81 in the ones column, so you carry 8. With two numbers the carry is always 0 or 1, because two digits plus a carry add up to at most 19.
How can I check a long addition answer?
Estimate first by rounding each number: 937 + 129 + 248 is about 900 + 100 + 200 = 1,200, so an answer of 1,314 is reasonable and 13,140 or 131 is not. Then add the numbers again in a different order (248 + 129 + 937) or add the column from the bottom up; the sum must be the same.
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This calculator is for educational purposes. Double-check important results before acting on them.