About the Long Addition Calculator
Column addition, also called long addition, is the written way to add several numbers by lining them up by place value and adding one column at a time from the right. This calculator lays the numbers out in columns, writes each carry above the column it goes into, and gives the total. Decimals are lined up on the point automatically. It is a simple way to check homework, a till float or a list of expenses, and to see exactly where a carry was needed.
Updated October 2026
How to use the Long Addition Calculator
- 1Type or paste the numbers, one per line.
- 2Check the total in the answer box.
- 3Look at the working: carries sit on the top line.
- 4Follow the columns from right to left.
- 5Copy the total if you need it.
A worked example
Adding 1,284 + 937 + 45: the ones column is 4 + 7 + 5 = 16, so write 6 and carry 1. The tens column is 8 + 3 + 4 + 1 = 16, write 6 and carry 1. The hundreds column is 2 + 9 + 1 = 12, write 2 and carry 1. The thousands column is 1 + 1 = 2. The total is 2,266.
Tips for accurate addition
Most mistakes come from columns that drift out of line or a forgotten carry.
- Write digits in neat columns, or use squared paper
- Line decimals up on the point and fill gaps with zeros
- Say each carry out loud and write it above the next column
- Check by adding the numbers in a different order
When the written method still matters
Mental and written addition are part of every school maths course, and many exams don't allow calculators. Seeing the carries laid out makes it clear why the method works: each column is worth ten times the one to its right.
Checking money and lists
Paste a list of prices or receipts to get an exact total without rounding. Because the tool uses exact decimal arithmetic, totals of pounds and pence or dollars and cents come out exactly, unlike some spreadsheet sums that show tiny rounding errors.
Teaching with it
Parents and teachers can type the numbers from a worksheet and show the carries one column at a time. Ask the child to predict each carry before looking, then compare. Because the layout matches the way the method is written on paper, it is easy to spot which step went wrong.
Phone or computer
The working uses a fixed-width font so columns stay aligned on any screen. Column addition is the base for other written methods. Continue with the Long Subtraction Calculator, the Long Multiplication Calculator, and the Long Division Calculator, which each show their steps in the same way.
Features
- Up to 20 numbers at once
- Carries shown above each column
- Decimals lined up on the point
- Commas in numbers are fine
- Exact arithmetic
- Copy the total
Frequently asked questions
How does column addition work?
Line the numbers up by place value, add the ones column first, write the last digit of that sum and carry any tens to the next column. Repeat for each column moving left.
What does carrying mean?
When a column adds up to 10 or more, you write the ones digit in that column and carry the tens digit into the next column on the left, where it is added in.
Can I add decimals?
Yes. The calculator lines the numbers up on the decimal point and fills empty places with zeros, so 37.5 + 2.75 = 40.25.
Can I paste a column from a spreadsheet?
Yes. Paste one number per line; thousands separators such as 1,284 are fine.
Does it work with negative numbers?
This tool is for adding positive numbers. To take one number away from another, use the long subtraction calculator.
Why is the carry line sometimes empty?
If no column adds up to 10 or more, nothing needs carrying.