Basic Calculator
A straightforward four-function calculator with percentage and sign change. Mouse, touch, or keyboard.
Runs entirely in your browser. Nothing is sent to our servers.
About this tool
A simple four-function calculator with percentage and sign-change. Works by mouse, touch, or keyboard. Designed to match how every desk calculator has worked since the 1970s — no hidden quirks, no surprises.
Keyboard shortcuts
- 0–9, . — enter digits
- +, -, *, / — operations
- Enter or = — evaluate
- Esc — clear
- Backspace — delete last digit
- % — percent
When to use which calculator
Use this one for everyday arithmetic — splitting a bill, adding up receipts, working out a discount. For multi-step math with parentheses and functions, use the Scientific Calculator. For working with fractions like 3/8 + 1/2, use the Fraction Calculator.
Frequently asked questions
- How does the percent key work?
- It treats the displayed number as a percentage and divides by 100. After "200 + 10 %" the calculator shows 220 — meaning "add 10% of 200 to 200". Different calculators implement this differently; this one matches the convention of most desk calculators.
- Why does the result use scientific notation sometimes?
- For very large or very small numbers, scientific notation (e.g. 1.5e+20) is more readable than 20 digits of decimal. JavaScript switches automatically.
- How precise is it?
- IEEE 754 double-precision floating point, about 15–17 significant digits. Tiny rounding errors can show up for some inputs (the famous 0.1 + 0.2 ≠ 0.3 problem). For exact decimal arithmetic, use a spreadsheet with appropriate formatting.
Last updated: May 17, 2026