Adding Machine Calculator
A classic adding machine in your browser: type numbers, add or subtract them in sequence, and watch the virtual paper tape record every entry with a running subtotal. Edit or delete any line, then copy or print the tape.
Keyboard: 0–9 · . · + − · Enter = total · S = subtotal · Backspace deletes a digit. Tap any tape line to edit it.
How to use it
- Type a number on the keypad (or your keyboard).
- Press + to add it to the tape or − to subtract it.
- Press SUB any time to print a subtotal line without clearing the tape.
- Press = to print the grand total — this clears the tape, like a real adding machine.
- Tap any tape line to edit it, or tap the ✕ to delete it. The running total recalculates instantly.
Worked example
You are totaling a grocery receipt: milk 4.20, bread 2.85, a 1.50 coupon (subtract), cheese 6.40.
| Key presses | Tape line | Running total |
|---|---|---|
| 4.20 + | + 4.20 | 4.20 |
| 2.85 + | + 2.85 | 7.05 |
| 1.50 − | − 1.50 | 5.55 |
| SUB | SUBTOTAL 5.55 | 5.55 |
| 6.40 + | + 6.40 | 11.95 |
| = | TOTAL 11.95 | — |
Note how 4.20 + 2.85 − 1.50 lands exactly on 5.55. This tool does all money math in whole cents, so you never see the classic 0.1 + 0.2 = 0.30000000000000004 floating-point glitch.
Why a virtual paper tape?
An ordinary calculator shows you only the last answer. If you mistyped the third of twelve numbers, you start over. A paper tape shows every entry, so you can audit, edit, or delete a single line and the total fixes itself.
This is the same workflow accountants and bookkeepers used on mechanical adding machines for a century: enter a column of figures, pull a subtotal mid-way, and print a grand total at the end. The difference here is that the tape is forgiving — no white-out required.
How the math works
- Every number is converted to whole cents (integer arithmetic) before anything is added.
- Digits beyond 2 decimal places round half away from zero (0.125 → 0.13), the standard cash-register rule.
- The tape total is the exact sum of the integer cents — no binary floating-point is ever used for money.
- Accepted input formats:
1,234.56,$1,234.56,(25.25)for negatives,-7.5. - Safe range: up to about 90 trillion (9×10¹³) in any currency unit — far beyond any real receipt or invoice.
Adding machine vs. regular calculator
A regular calculator (see our arithmetic calculator) evaluates one expression at a time: 4.20 + 2.85, answer, done. An adding machine is built for sequential entry:
- A persistent, printable paper tape of every operation.
- Running subtotal without clearing the tape.
- Grand total that clears the tape for the next job.
- Per-line edit and delete instead of starting over.
If you need multiplication, division, or parentheses, use a regular calculator. If you need to total a column of numbers with an audit trail, you are in the right place.
Frequently asked questions
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