Calculator
This free online calculator covers the four operations you actually use every day — addition, subtraction, multiplication and division — with a running expression line, a percent key, sign toggle, and full keyboard support. It is the plain standard calculator layout with nothing hidden: no unit conversions, no history pruning you have to undo, no settings. Type with the mouse or just start typing with the keyboard; the expression line shows what you have entered and the result line updates as you go. If you need percentages as a concept rather than a single key, the percentage calculator walks through all five percentage questions step by step.
What This Online Calculator Does
The tool is deliberately small, and it is worth being precise about the scope, because “calculator” means different things on different pages:
- Arithmetic: +, −, × (typed as
*), ÷ (typed as/), decimal point, parentheses are not supported — this is a basic calculator, not an expression parser. - Percent key: divides the number currently on screen by 100. That is the whole behaviour, and it is stated below with worked examples so the key never surprises you.
- Sign toggle (+/−): flips the sign of the displayed number.
- C / CE and Backspace: CE clears the current entry, C clears everything, Backspace deletes the last character.
- Scientific notation entry: the letter
eis accepted, so1e3is 1000.
Anything outside that set is rejected on purpose. Division by zero, unknown characters and results that overflow floating point all end in a clear message in the display area — the tool never leaves a silent Infinity or NaN on screen — and the message reads Error while the result resets to 0, so the next calculation starts clean.
The Formula Behind Every Key
Under the surface the calculator evaluates exactly the expression you typed, in the order the operators imply, with the usual precedence of multiplication and division over addition and subtraction when you chain them:
\[ a + b \]
\[ a – b \]
\[ a \times b \]
\[ a \div b \;\; (b \neq 0) \]
Percent is defined as one division and nothing else:
\[ x\% \;\rightarrow\; \frac{x}{100} \]
That single rule is worth spelling out because calculator apps differ: some treat “200 + 15%” as a 15% increase (230), while this one converts 15% to 0.15 first and then adds, giving 200.15. Both conventions exist in the wild; this calculator follows the second one, and the worked examples below show the exact keystrokes and the exact display so there is no ambiguity. If the increase-by-a-percentage case is what you need, the percentage calculator’s “increase by” mode is built for it.
Precision and display. The result line prints the value as JavaScript computes it, trimmed of floating-point noise: a result with decimals is rounded to at most ten decimal places and trailing zeros are dropped, so 0.1 + 0.2 shows 0.3 rather than 0.30000000000000004. Integers print without a decimal point, and the calculator is unit-agnostic: the same arithmetic works whatever the numbers represent, whether you are adding centimetres or inches, kilograms or pounds, dollars or euros. Division by zero is refused with the message “Division by zero” instead of returning infinity, and a negative zero is never displayed as −0.
How to Use the Calculator
- Click the number buttons, or just type the digits — the same handlers serve both, so the keyboard works immediately without clicking any field first. Digits 0–9,
+,-,*,/and.all map to the corresponding buttons. - Press
Enteror=to evaluate. The expression moves out of the way and the result stays on the result line, ready to be used as the starting value of the next calculation. - Press
%to divide the current number by 100. The +/− button flips the sign.Escapeclears everything;Backspacedeletes one character. - Read the two lines: the top line shows the running expression (for example
200+), the bottom line shows either the number you are typing or the latest result. - If the display shows Error, the input was rejected — a zero divisor or an unsupported character. The reset to 0 happens automatically, so you can start the next sum immediately.
Worked Examples
Example 1 — an addition that includes a percent key press
Type 200, press +, type 15, press %, then =. The percent key turns 15 into 0.15, and the expression 200 + 0.15 evaluates to 200.15. The expression line reads 200+15% while you are typing it; after Enter, the result line holds 200.15 and the expression line is cleared.
Example 2 — a percentage of an amount
Type 1250*0.08 — 1250, the times key, then 0.08 — and press =: 100. Multiplying by a decimal is the most reliable way to take a percentage of something on a basic calculator, because it makes the arithmetic explicit — 8% of 1250 is 1250 × 0.08. Typing 1250*8% instead gives 1250 × 0.08 as well, because the percent key converts the 8 to 0.08; both routes agree, and either is fine.
Example 3 — a division that must not divide by zero
Dividing by zero is undefined, not infinite, so the calculator refuses it: type 5, press /, type 0, press = and the display shows Error, then resets the result to 0. The same applies to a zero written as 0.0. The check exists because a silent Infinity would propagate through the next calculation and look like a real number.
| Symbol | Meaning | On the keypad |
|---|---|---|
| + | addition | plus key or keyboard + |
| − | subtraction | minus key or keyboard - |
| × | multiplication | times key; on the keyboard press * |
| ÷ | division (divisor must be non-zero) | divide key; on the keyboard press / |
| % | divide the current number by 100 | percent key or keyboard % |
| ± | change sign | +/− button |
| C / CE | clear all / clear current entry | buttons or Escape for C, Backspace for one character |
Calculator FAQ
Does this calculator work on a phone?
Yes. The buttons are ordinary touch targets and the layout reflows to the screen width, so the same tool serves as a phone calculator without an app install. The keyboard shortcuts described above are a convenience on desktop; on a phone you simply tap the keys.
Is it a free calculator — no sign-up, no limits?
It is free and needs no account. All arithmetic runs in your browser: nothing you type is sent anywhere, there is no calculation counter and no rate limit, and the page keeps working offline once it has loaded because the calculator itself makes no network requests.
Why does 200 + 15% give 200.15 and not 230?
Because the percent key is defined as “divide the current number by 100”: 15 becomes 0.15, and 200 + 0.15 = 200.15. Calculators differ on this convention; if you want “increase 200 by 15%” as a single operation, use the percentage calculator’s increase mode, which computes 200 + 200 × 15 ÷ 100 = 230 and shows the working.
Can I use the result of one calculation in the next?
Yes — after pressing = the result stays on the result line and becomes the first number of the next expression, exactly like a desk calculator. Pressing an operator right after a result continues from it; pressing C starts over from zero.
Does it support parentheses, powers or square roots?
No. This is intentionally a standard four-operation calculator, and it rejects characters outside digits, the four operators, the decimal point and scientific notation. For roots, powers and multi-step expressions, a scientific calculator is the right tool; for everyday sums, the smaller set of keys is faster to use and impossible to misconfigure.
Why does the display show Error instead of a number?
Two inputs are rejected: division by zero, and any character the parser does not recognise. In both cases the result resets to 0 and the next calculation can start immediately. This is deliberate — returning Infinity or quietly ignoring bad input produces a wrong number that looks right, which is worse than a visible error.
Related Tools
If the calculation you need is about percentages rather than plain arithmetic, the percentage calculator covers percent-of, percent-change and increase/decrease with the working shown. For picking numbers rather than computing them, the random number generator draws integers in any range. And if the numbers you are checking are health figures, the BMI calculator and the other health tools on BunTool do that arithmetic with the right formulas and units.
