Basic Calculator
A free, fast online calculator — add, subtract, multiply, divide, percentages and sign toggle, with full keyboard support. No signup, runs in your browser.
Basic Calculator
Tip: use your keyboard — digits, + − * /, Enter to equal, Esc to clear.
How to Use the Basic Calculator
Enter a number
Tap the digit buttons or just type on your keyboard. The display shows your number with thousands separators so large figures stay readable.
Pick an operation
Choose add, subtract, multiply, or divide, then enter the next number. You can chain as many operations as you like — the calculator evaluates left to right, like a classic pocket calculator.
Use percent and sign
The % key works in context — type 200 + 10 % and it adds 10% of 200. The ± key flips the sign of the current number. ⌫ deletes the last digit; AC clears everything.
Get the answer
Press = (or Enter) to see the result. Need more? When you have an answer, the calculator suggests the next logical tool — like turning the result into a percentage.
The Calculator, Reconsidered
Why a Plain Calculator Still Matters
Most people who open a calculator want a fast, no-nonsense place to add a few numbers, split a bill, work out a tip, or check a sum. It sounds almost too simple to think about, yet a good basic calculator is a small piece of craft. It has to feel instant, never lose your place, format big numbers so they are readable, and behave exactly the way a physical pocket calculator does — because that is the mental model nearly everyone carries. This calculator is deliberately faithful to that model: it evaluates left to right rather than applying algebraic operator precedence. Type 2 + 3 × 4 here and you get 20 (it adds 2 and 3 to make 5, then multiplies by 4), exactly as a desk calculator would. If you want 14 — multiplication first, the algebra convention — that is what the Scientific Calculator is for, and a tap away.
The percent key is the other place pocket calculators have a specific, learned behaviour, and getting it right matters. Press 200 + 10 % and the answer is 220, because the calculator interprets "10%" in the context of the running total — it adds ten percent of 200; 200 − 10 % likewise gives 180. Used on its own, 50 % simply becomes 0.5. That add-on / discount behaviour is the one desk calculators have taught for decades. It is the only percent convention this page implements — see the FAQ before combining % with × or ÷. The display formats results with grouped thousands and handles the full keyboard, so you can work as fast as you think without reaching for the mouse.
"The hardest tool to design is the one everyone already knows how to use. A basic calculator has no learning curve — which means every detail has to match the model in the user's head."
Part of a Bigger Math Toolkit
This calculator is the front door to a whole connected family of math tools. Its arithmetic is ordinary double-precision floating point — the IEEE 754 binary64 format that every JavaScript engine, spreadsheet and pocket-calculator app shares — so its answers agree with those tools digit for digit. The moment you need something more — to turn a result into a percentage, to round it cleanly, to factor a number, or to switch to full scientific functions — the next tool is one click away, often with your number already carried across so you do not retype anything. For the everyday jobs, though — sums, differences, products, quotients, a quick percentage — this page is all you need: it loads instantly, works offline once open, and never sends a single keystroke to a server.
This one reads left to right, so 2 + 3 × 4 is 20
Whole numbers are exact up to 9,007,199,254,740,991 (2⁵³ − 1, the largest safe integer in IEEE 754 binary64); add 1 beyond it and the sum may not change.
A basic calculator evaluates left to right, not by algebraic precedence.
So 2 + 3 × 4 gives 20 here, but 14 on a scientific calculator.
The % key is contextual: 200 + 10% means "add 10% of 200" = 220.
0.1 + 0.2 shows 0.30000000000000004, because a tenth has no finite binary expansion — the case Goldberg's 1991 ACM survey made famous.
Dividing by zero shows Error: IEEE 754 would return ∞, but a pocket calculator says E, and this page follows the calculator.
The word "calculator" comes from the Latin calculus — a small pebble used for counting.
This tool supports the full keyboard — including Enter to equal and Esc to clear.
It runs entirely in your browser — no keystroke is ever uploaded.
Pressing = again repeats the last operation — 5 + 3 = = gives 11 — the way desk calculators behave.
Frequently Asked Questions
- Because a basic calculator evaluates left to right, like a physical pocket calculator: it adds 2 and 3 to get 5, then multiplies by 4 to get 20. The algebraic convention "multiply before add" (which gives 14) is what the Scientific Calculator uses — switch to it if you want operator precedence and parentheses.
- It is contextual, matching pocket-calculator behaviour. Press
200 + 10 %and it computes 10% of 200 (= 20) and adds it, giving 220. Used on its own,50 %just becomes 0.5. For more advanced percentage work — finding what percent one number is of another — use the dedicated Percentage Calculator. - Yes — full keyboard support. Type digits and the operators + − * /, press Enter (or =) to calculate, Backspace to delete the last digit, and Esc to clear everything. You never have to reach for the mouse.
- AC (all clear) wipes everything — the current number, the running total, and the pending operation — back to zero. ⌫ (backspace) just deletes the last digit you typed, so you can fix a typo without starting over.
- Yes. Use the decimal point button (or the period key) for decimals, and the ± key to flip the sign of the current number between positive and negative. Results are shown with grouped thousands for readability.
- Division by zero is undefined in mathematics, so the calculator shows "Error" rather than a misleading number. Press AC to clear and continue. This matches how physical calculators handle the same situation.
- Completely. Everything runs in your browser — no keystroke, number, or result is uploaded, stored, or logged. The calculator even works offline once the page has loaded. It is as private as a physical calculator on your desk.
- Yes — this is the entry point to a whole family of connected math tools. For sin/cos/log, powers, parentheses and operator precedence, use the Scientific Calculator. For fractions, percentages, rounding, prime factors, and more, the related tools are one click away, often with your number carried across automatically.
- Whole-number sums, differences and products are exact up to 9,007,199,254,740,991 (2⁵³ − 1). Decimal fractions are stored in binary (IEEE 754 binary64, the number format of every JavaScript engine), so a few results carry a trailing rounding digit —
0.1 + 0.2displays as 0.30000000000000004 rather than 0.3. That is a property of floating-point arithmetic shared by spreadsheets and programming languages, not an error in the sum; read the result to the decimals you need. - No. The percent key here implements the add-on / discount convention only:
200 + 10 %gives 220 and200 − 10 %gives 180. After × or ÷ the key still converts the second number into a percentage of the first, so200 × 10 % =evaluates 200 × 20 = 4,000 — not the 20 a desk calculator shows. To take a percentage of a number, multiply by the decimal (200 × 0.1) or use the Percentage Calculator.
Method & sources
How it computes
Four-function chain calculator: operations are applied strictly left to right as they are entered (2 + 3 × 4 = 20), with no operator precedence, using IEEE 754 binary64 arithmetic as defined for the ECMAScript Number type. The percent key converts the current entry to a percentage of the running total (200 + 10 % = 220; 50 % alone = 0.5); division by zero displays Error; pressing = again repeats the last operation.
What this tool implements
- Chain (left-to-right) evaluation, the desk-calculator convention, rather than the algebraic precedence of ISO 80000-2 — stated on the page with the 2 + 3 × 4 = 20 example; the Scientific Calculator is the algebraic tool.
- Arithmetic and display follow the ECMAScript Number type (IEEE 754-2019 binary64): integers exact to 2⁵³ − 1 = 9,007,199,254,740,991; non-terminating binary fractions such as 0.1 + 0.2 display their rounded double (0.30000000000000004); the page now says so instead of claiming exactness.
- Percent key implements the add-on / discount convention only (a + b % = a(1 + b/100), a − b % = a(1 − b/100)); the page states that × and ÷ do not follow the desk-calculator rule.
- Division by zero, which IEEE 754 defines as ±∞ or NaN, is shown as Error, matching pocket-calculator behaviour.
Sources
- Ecma International. ECMA-262: ECMAScript Language Specification. 17th ed. Geneva: Ecma International; 2026. §6.1.6.1 The Number Type (IEEE 754-2019 binary64 values and rounding). https://ecma-international.org/publications-and-standards/standar…
- IEEE Std 754-2019. IEEE Standard for Floating-Point Arithmetic. New York: IEEE; 2019. https://standards.ieee.org/ieee/754/6210/
- Goldberg D. What every computer scientist should know about floating-point arithmetic. ACM Computing Surveys 1991;23(1):5-48. https://doi.org/10.1145/103162.103163
- Knuth DE. The Art of Computer Programming, Volume 2: Seminumerical Algorithms. 3rd ed. Reading, MA: Addison-Wesley; 1998. §4.2 Floating-point arithmetic.
What can make this go out of date
- None at runtime — pure arithmetic; no rates, tables or published series.
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