Long Addition Calculator
Enter any numbers separated by commas and see the sum instantly. The step-by-step panel works through each column from right to left, showing every carry digit, exactly as you would do it by hand on paper. Whole numbers and decimals are both supported.
Formula
Worked example
Add 937, 129, and 2248. Ones column: 7 + 9 + 8 = 24, write 4 carry 2. Tens column: 3 + 2 + 4 + 2 (carry) = 11, write 1 carry 1. Hundreds column: 9 + 1 + 2 + 1 (carry) = 13, write 3 carry 1. Thousands column: 2 + 1 (carry) = 3. Sum = 3314.
What is long addition?
Long addition is the standard written method for adding two or more numbers of any size. You stack the numbers with their place values aligned (ones under ones, tens under tens, and so on), then add each column from right to left. When a column totals more than 9, you write down the units digit and carry the tens digit to the next column on the left. This process works for whole numbers and for decimals, where you align decimal points instead of right-aligning.
How to do long addition step by step
Write the numbers in a vertical stack, aligning decimal points (or right-aligning whole numbers). Pad any number with fewer decimal places by adding trailing zeros so all rows have the same width. Starting from the rightmost column, add every digit in that column plus any carry from the previous column. Write the units digit of the result below the column and carry any tens digit to the next column on the left. Repeat for every column moving left. If a carry remains after the leftmost column, write it as a new leading digit. The bottom row is the sum.
Understanding carries
A carry occurs whenever the digits in a single column add up to 10 or more. For example, if the ones column contains 7, 6, and 9, their total is 22. You write 2 in the ones place and carry 2 to the tens column. The carry is typically written as a small superscript digit above the next column so you do not lose track of it. If carries accumulate across several adjacent columns, work them in sequence from right to left, including each carry in that column's total before moving on.
Long addition with decimals
Decimal long addition follows exactly the same rules as whole-number long addition. The only extra step is alignment: line up the decimal points vertically before you start. Pad shorter numbers with trailing zeros so every row has the same number of decimal places. Once the columns are aligned, add from the rightmost decimal digit all the way through the integer part, carrying as needed. The decimal point in the answer sits directly below the decimal points in the addends.
Place value chart for long addition
| Column position | Place value | Worth | Digit 5 represents |
|---|---|---|---|
| Rightmost whole-number | Ones | 10^0 = 1 | 5 |
| 2nd from right | Tens | 10^1 = 10 | 50 |
| 3rd from right | Hundreds | 10^2 = 100 | 500 |
| 4th from right | Thousands | 10^3 = 1,000 | 5,000 |
| 5th from right | Ten-thousands | 10^4 = 10,000 | 50,000 |
| 1st after decimal | Tenths | 10^-1 = 0.1 | 0.5 |
| 2nd after decimal | Hundredths | 10^-2 = 0.01 | 0.05 |
| 3rd after decimal | Thousandths | 10^-3 = 0.001 | 0.005 |
Each column position represents a power of ten. Carry digits always move one column to the left.
Frequently asked questions
How many numbers can I add at once?
You can add as many numbers as you like. Separate them with commas or spaces in the input box. The calculator will parse every valid number and add them all.
Can I add decimal numbers?
Yes. Use a period (.) as the decimal separator. The calculator aligns the decimal points automatically and shows the carry steps for each decimal column as well as each integer column.
What is a carry in long addition?
A carry is the digit that moves to the next column when a column total reaches 10 or more. For example, 7 + 6 = 13, so you write 3 in that column and carry 1 to the column on the left. The carry gets added in when you total that next column.
Does the order of the numbers matter?
No. Addition is commutative, meaning the sum is the same regardless of the order you list the addends. Rearranging the numbers can sometimes make mental checking easier (for instance, grouping pairs that sum to a round number), but it does not change the answer.
How do I add numbers with different numbers of digits?
Right-align the numbers (or align decimal points for decimals), then pad the shorter numbers with leading zeros if it helps visualize the columns. A 3-digit number added to a 5-digit number simply has two implicit leading zeros. Once aligned, proceed column by column as usual.
What is the difference between long addition and mental addition?
Long addition is a written, column-by-column method that handles any size of number systematically. Mental addition relies on number sense and shortcuts such as rounding and decomposing numbers, and it is faster for small or friendly numbers but harder to verify for large or irregular ones. Long addition is the standard method taught in schools because it is reliable and every step can be checked.