# Basic Calculator - Add, Subtract, Multiply, Divide Free online four-function desk calculator with percent, sign change, and square root. Sequential two-register arithmetic in your browser - not a PEMDAS expression engine. ### Keypad and Display Display _0_ C ⌫ % ÷ 7 8 9 × 4 5 6 − 1 2 3 + ± 0 . = √ Clear Copy Two-register desk arithmetic: operations run in the order you press them, not PEMDAS. Keyboard: digits, + − × ÷, Enter, Escape, Backspace. ### History and Result Details Copy Clear Current display 0 Equals and chained operators will list the last eight results here ### What Is a Basic Calculator and Why Use a Two-Register Model? A **basic calculator** (also called a four-function calculator) adds, subtracts, multiplies, and divides. This page also includes the extras that sit on almost every desk unit: **percent**, **sign change (±)**, and **square root**. What it does not do is parse a typed algebraic sentence. There is no hidden stack of parentheses and no PEMDAS reorder of the keys you already pressed. That design is intentional. Hardware from the 1970s onward stored a pending left operand in one register, an operator, and the number currently on the display. Pressing + after 12 parks 12 and waits for the next value. Pressing = (or another operator) finishes that pending pair. If you key 2 + 3 × 4, the machine computes (2 + 3) first, then multiplies by 4, and you get 20 - not 14. Students who grew up on phone “expression” calculators are often surprised. This **free online basic calculator** behaves like the plastic unit in a classroom supply closet so homework that says “use a four-function calculator” matches what you see. Everything runs in the browser. Digits never leave your device. After the page loads, a dropped network does not stop arithmetic. The last display, pending operator, and recent history lines are stored locally for up to 30 days so a refresh does not wipe a chain you were checking. ### How to Use This Free Online Basic Calculator Using this **two-register desk calculator** is the same muscle memory as a physical keypad: 1. **Enter a number** with the digit keys or your keyboard. One decimal point is allowed. ± flips the sign of whatever is on the display. 2. Press an **operator** (+, −, ×, or ÷). The current value is stored as the pending left operand. 3. Enter the second number and press **=**. To chain, press another operator instead of equals: the pending pair is finished first, then the new operator is armed. 4. Use **%** as a percent of 100, or as a percent of the pending register when an operator is already set. Use **√** only on a non-negative display. **C** or Escape clears the registers. **⌫** or Backspace deletes the last digit while you are still typing a number. **Note:** divide by zero is an error, not Infinity. Press C to recover. The display accepts at most 16 characters while you type. ### Sequential Arithmetic vs. PEMDAS - Worked Key Sequences left op right → display One pending operator at a time, in key order #### Example - 12 + 3 = 15 - Type 12, press +, type 3, press = - History records **12 + 3 = 15** #### Example - why 2 + 3 × 4 is 20 here - 2 + stores 2 with addition pending - 3 × finishes 2 + 3 = 5, then arms multiply - 4 = finishes 5 × 4 = **20** - An algebraic engine would have done 2 + (3 × 4) = 14. Use a scientific or expression calculator when a worksheet requires that grouping. #### Example - percent of a pending amount - 200 + 10 % turns the 10 into 10% of 200, which is 20 - Then = yields 220 (a 10% increase, desk-calculator style) - With no pending operator, 25 % simply becomes 0.25 Long division with a remainder, or rewriting a decimal as _a × 10n_, is a different job. Open the [long division calculator](https://www.toolcomb.com/long-division-calculator) or the [scientific notation calculator](https://www.toolcomb.com/scientific-notation-calculator) when you need those formats instead of a running total. ### Percent, Sign Change, Square Root, and Zero **Percent** on four-function hardware is not a spreadsheet formula. If an operator and a left operand are already stored, the current display is treated as a percentage of that pending value: current ← acc × (current / 100). Otherwise the display is divided by 100. That matches the “tax” and “discount” sequences people learned on desktop machines, and it is why 200 + 10 % is not the same as typing 200 + 0.10 unless you meant a raw addend of a tenth. **±** only negates the number you are looking at. It does not reverse the pending operator. **√** uses `Math.sqrt` on the current display. A negative radicand is an error; this page does not invent imaginary results. Division by zero is also an error string - _Cannot divide by zero_ - so you never copy Infinity into a lab notebook. When you need the mean of a list rather than a running four-function total, switch to the [average calculator](https://www.toolcomb.com/average-calculator). A desk calculator can add scores one at a time; it will not report median, mode, or range unless you do that extra work by hand. ### Frequently Asked Questions (FAQ) - Basic Calculator #### How do I use a basic online calculator? Enter a number, tap an operator (+, −, ×, ÷), enter the next number, then press equals. Chain more operators if you want sequential results. Percent, ±, and square root act on the value currently on the display. #### Does this calculator follow PEMDAS or order of operations? No. It is a two-register desk calculator, not an expression parser. 2 + 3 × 4 is evaluated as (2 + 3) × 4 = 20 if you press the keys in that order, not as 2 + 12 = 14. Use a scientific or expression calculator when you need PEMDAS. #### What happens if I divide by zero on this calculator? Division by zero is an error. The calculator does not return Infinity or a fake number. Clear the display and continue with a non-zero divisor. #### How does the percent key work on a basic calculator? Percent typically treats the current display as a percentage of 100 (so 25% becomes 0.25) or, after an operator, as a percentage of the pending register - the same pattern as most four-function desk calculators, not as a programmable spreadsheet formula. #### Is this a scientific calculator or a four-function calculator? It is a basic (four-function plus percent, ±, and square root) calculator. There is no sin, log, memory stack, or typed algebraic expression. For those, use a scientific calculator instead. #### Does this basic calculator store my calculations online? No. Arithmetic runs in your browser with JavaScript. Nothing is sent to a server. After the page loads, the tool still works if the network drops. ### Why Choose Our Basic Calculator? - **Free, no account.** Unlimited four-function arithmetic. - **Private.** All math stays in the browser. - **Classic two-register behavior** so classroom “calculator” instructions match the keys. - **Honest divide-by-zero handling** - an error message, never Infinity. - **Percent, ±, and square root** on the same layout as a desk unit. - **Keyboard support** for digits, operators, Enter, Escape, and Backspace. - **Local history** of the last eight completed lines. ## Related Tools Discover more free tools that might help with your next task. 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