Long addition & subtraction (decimal carry/borrow)

How to use (3 steps)

Choose add or subtract, then type the two numbers. Commas and full-width digits are accepted.
Expand “Options” to keep trailing zeros or show guide lines. Teacher mode thickens lines and fixes the step panel for projection.
Click Calculate or just change an input to update the result, layout, and step-by-step narration. Use Auto play or the arrows to walk through each column.

Result

Shortcuts: Alt+S share, Alt+L copy LaTeX, Alt+[ previous step, Alt+] next step.

Teacher mode thickens fonts and lines, keeps the step list visible, and pairs well with projectors or screen recordings.
Use “Copy LaTeX” to paste a clean vertical layout into worksheets. The shareable URL preserves the inputs and options.
Auto play advances roughly every 2–3 seconds so students have time to read each step; you can pause anytime or step manually with the arrows.

How do I align decimals?

The tool pads the shorter decimal with zeros so both numbers share the same decimal length. Turn on the dotted decimal guide to see the alignment.

When do carry and borrow happen?

A carry appears when a column adds to 10 or more; a borrow appears when the top digit is smaller than the bottom digit plus any previous borrow.

How do you borrow through zeros?

We walk left until we find a non-zero digit, reduce it by one, and turn any zeros in between into 9s. Each borrow is shown in the steps.

Can I enter commas or full-width numbers?

Yes. Commas are removed, and common full-width digits and punctuation are normalized before checking the number.

Is anything sent to a server?

No. Everything runs locally. Only if you copy a shareable URL will the inputs appear in the link.

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