Adding Machine Calculator
A running tape you can read back: every step stays on screen, so you can check the work and copy it — not just the answer.
Tape
Start typing. Every step stays here so you can read the work back — and copy it.
Adds left to right, like a paper tape — so 2 + 3 × 4 is 20, not 14.
How to use
- Type or click — the keyboard works: digits, + − * /, Enter for equals, % for percent, Backspace, Escape to clear everything.
- Every operation lands on the tape above the display, so the running work stays visible instead of vanishing behind one number.
- Copy the tape when you're done — useful when you're adding up receipts, splitting bills, or checking somebody else's arithmetic.
How it works
Most calculators throw the work away. You press the keys, a number appears, and if it looks wrong you have no way to find out where it went wrong — you just start again and hope.
An adding machine keeps the tape. Every operand and operator stays on screen, with a double rule above each result, so the answer arrives with its own audit trail. That's the whole idea behind this site, in its simplest possible form: a number is only as good as the work you can check.
Two things worth knowing. It adds left to right, like the paper machine it imitates — so 2 + 3 × 4 is 20, not 14. And results are rounded to 12 significant digits, which is why 0.1 + 0.2 shows the 0.3 you expect rather than the 0.30000000000000004 that binary floating point actually produces.
Frequently asked questions
What is an adding machine calculator?
A calculator that keeps a running tape — the paper roll on an old office adding machine. Each entry and operation stays printed above the display, so instead of trusting a single number you can read back every step that produced it. It's the right tool whenever the trail matters more than the speed: reconciling receipts, checking an invoice, adding a long column of figures without losing your place.
Does it follow order of operations?
No — and that is deliberate. Like a physical adding machine, it evaluates left to right, so 2 + 3 × 4 gives 20, not 14. That's the convention people expect when they're running a column of figures. If you need algebraic precedence, use a scientific calculator instead; we'd rather tell you plainly than quietly give you a number you'd misread.
How does the % key work?
It follows the standard calculator convention: with + or −, the percent is taken of the running total (50 + 10% = 55, because 10% of 50 is 5). With × or ÷, it's simply a fraction (200 × 10% = 20). Pressed on its own, it divides by 100.
Why does 0.1 + 0.2 give exactly 0.3 here?
Because we round results to 12 significant digits before showing them. Computers store decimals in binary, where 0.1 + 0.2 is famously 0.30000000000000004 — mathematically noise, but alarming to read on a calculator. The tape records the same rounded figure you see, so reading the tape back reproduces the same answer.
Can I copy the tape?
Yes — the Copy tape button puts the whole run on your clipboard as plain text, ready to paste into an email, a spreadsheet, or a note to whoever's going to ask how you got that number.
Is anything I type sent anywhere?
No. The calculator runs entirely in your browser. Nothing you type is uploaded, stored on a server, or visible to us.