How long addition works
- Stack the numbers with their units digits aligned on the right.
- Add the right-most column. Write the units digit of that sum at the bottom; if it's two digits, carry the tens digit into the next column.
- Move one column left and add — including any carry from the previous column.
- Continue until you've added the leftmost column. Any final carry becomes the leading digit of the total.
columnk: sum = (digits in column) + carryk-1; write sum mod 10, carryk = ⌊sum / 10⌋
FAQ
How many numbers can I add?
As many as you like — one per line. The calculator also accepts comma- or space-separated values.
What about negative numbers?
Mix positive and negative numbers and the total will reflect the algebraic sum. The column working is shown on the absolute totals and the sign attached to the result.
Can I add decimals?
Yes — decimal points are aligned automatically before the column working is computed.