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Basic Calculator — Free Online Calculator

Perform standard arithmetic operations with a simple interface

Ready for calculation...
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Basic Calculator: Free Online Arithmetic Calculator

Table of Contents - Basic

How to Use This Calculator - Basic

The calculator presents a clean interface with a dark display area at the top showing your current expression and result. Below the display is a grid of buttons arranged in rows.

The top row contains C (clear all), CE (clear entry—erases just the last number entered), a backspace button (⌫) for deleting the last digit, and the division symbol (÷).

The next three rows contain the number pad (7-8-9, 4-5-6, 1-2-3) with operation buttons on the right: multiplication (×), subtraction (−), and addition (+).

The bottom row has a wide zero button spanning two columns, a decimal point, and the equals button (=).

As you type, the display shows your running expression. Click equals or press Enter to see the result. The expression area shows the full calculation (like "15 + 23 × 2 = 61") so you can verify what was computed.

You can use your keyboard for input: number keys, +, -, *, /, Enter for equals, and Backspace or Delete to clear.

The Core Principle: Order of Operations

Calculators don't simply work left to right. They follow PEMDAS (or BODMAS in the UK): Parentheses, Exponents, Multiplication and Division, Addition and Subtraction.

This means 5 + 3 × 2 equals 11, not 16. The multiplication happens before the addition: 3 × 2 = 6, then 5 + 6 = 11.

Understanding this principle prevents the most common calculator frustrations. If you want 5 + 3 calculated before multiplying by 2, you'd need parentheses: (5 + 3) × 2 = 16. This basic calculator follows standard order of operations, giving you predictable, mathematically correct results.

The equals key serves as the final instruction to compute everything entered so far. Until you press equals, you're building an expression. After equals, you see the result.

How to Perform Calculations Manually

Addition and subtraction:

These are straightforward—combine values from left to right. 45 + 23 - 12 = 56

Multiplication and division:

These take precedence over addition and subtraction. 20 + 4 × 5 = 20 + 20 = 40 (not 120)

Chain calculations:

Many real-world problems involve multiple operations.

Example: You buy 3 items at £12.99 each and pay with a £50 note. What's your change?

50 - 3 × 12.99 = 50 - 38.97 = 11.03

Working with decimals:

Enter the decimal point between whole and fractional parts. 15.75 + 8.25 = 24.00

Negative numbers:

For entering a negative number, type the positive version and change the sign, or start with subtraction from zero. 0 - 15 + 20 = 5

Real-World Applications

Budgeting and personal finance. Quickly add up expenses, calculate remaining budget, or figure out how costs divide among people. Adding receipts, subtracting from account balances, and checking totals are everyday calculator tasks.

Shopping calculations. Figure out unit prices, calculate discounts, compare deals, or estimate totals before checkout. "This 500g package costs £4.50, but the 750g is £6.00—which is cheaper per gram?"

Tip and bill splitting. Calculate 15% or 20% tip on a restaurant bill, then divide the total among diners. A common sequence: bill amount × tip percentage, add to bill, divide by number of people.

Home improvement math. Calculate how many tiles you need (area ÷ tile size), figure out paint coverage (wall area × coats needed), or estimate material costs (quantity × price per unit).

Checking homework. Verify arithmetic homework answers, practice mental math by predicting then checking, or work through multi-step word problems with a calculator sanity-check.

Scenarios People Actually Run Into

The "wrong answer" that isn't wrong. You typed 10 + 5 × 2 expecting 30, but the calculator says 20. The calculator is right—multiplication precedes addition. You meant (10 + 5) × 2, which requires parentheses (not available on this basic calculator, but the concept explains the discrepancy).

Forgetting the order of entry. You're adding a long list of expenses but lose track. Did you already add the £35 item? The expression display helps here—scroll through what you've entered to verify.

The running total confusion. After calculating 15 + 20 = 35, you want to add another 10. You can continue: + 10 = gives 45. But if you start fresh with 10 +, you've lost the previous total.

Decimal precision surprises. 10 ÷ 3 gives 3.333... How many decimals should you use? For money, round to 2 decimal places. For measurements, context determines precision. The calculator shows more precision than you usually need.

The division by zero trap. Entering 5 ÷ 0 produces an error or infinity symbol. Division by zero is mathematically undefined. If you get this unexpectedly, check that your divisor is actually non-zero.

Trade-Offs and Decisions People Underestimate

Precision versus readability. The calculator might show 8 decimal places for a simple division. You'll need to round for practical use. Money rounds to pennies. Measurements might round to eighths or sixteenths.

Mental math versus calculator dependency. Using a calculator for every small arithmetic operation can atrophy mental math skills. Balance convenience with practice. Estimate first, then verify with the calculator.

Order of operations awareness. Many people never learned or forgot PEMDAS. Basic calculators assume you know it. If your results seem wrong, order of operations is usually the culprit.

Calculator versus spreadsheet. For one-off calculations, a calculator is faster. For recurring calculations, or ones you need to document and modify, a spreadsheet is more appropriate. A calculator doesn't save your work.

Physical versus digital calculators. This online calculator works anywhere with internet access. A physical calculator or phone app works offline. Neither is universally better—context determines which is more convenient.

Common Mistakes and How to Recover

Pressing equals too early. You're midway through 45 + 23 and accidentally press equals, getting 68 when you meant to continue adding. Solution: if you remember what you were doing, enter 68 + [remaining numbers]. The result becomes your new starting point.

Clearing when you meant to clear entry. You typed 45 + 23 + 1 (meant to type 10, not 1). Pressing C clears everything; CE clears just the 1 so you can type 10. Know which is which.

Forgetting the decimal point. You meant 12.99 but typed 1299. The result is 100× too large. Re-enter carefully. There's no quick fix once the wrong number is embedded in a calculation.

Double-tapping operators. You type 45 + + 23, accidentally hitting plus twice. Most calculators ignore the duplicate or replace the first operator with the second. But it can cause confusion if you're not watching the display.

Losing track of the calculation. After several operations, you're not sure what you've entered. The expression display shows your history. If in doubt, clear and start over—it's faster than troubleshooting a confused calculation.

Related Topics

Percentage calculations. Many basic calculators have a % key (this one doesn't prominently feature it, but the concept applies). To find 15% of 200, calculate 200 × 0.15 or 200 × 15 ÷ 100 = 30.

Scientific calculators. For exponents, trigonometry, logarithms, and more complex operations, you need a scientific calculator. Basic calculators handle arithmetic; scientific calculators handle mathematical functions.

Memory functions. Some calculators have M+, M-, MR, and MC for storing and recalling values. This helps with multi-step problems where you need to store an intermediate result while computing something else.

Floating-point precision. Computers represent decimals in binary, which introduces tiny rounding errors. 0.1 + 0.2 might equal 0.30000000000000004 rather than exactly 0.3. For everyday arithmetic, this is invisible, but it explains occasional strange decimal results.

Spreadsheet formulas. The same arithmetic principles apply to spreadsheet formulas. =A1+B1*C1 in a spreadsheet follows the same order of operations as a calculator would.

How This Calculator Works

The calculator uses JavaScript to process your input in real time. As you press buttons or type keys, it builds a string representation of your expression.

When you press equals, the calculator parses the expression, applies order of operations, and evaluates the result. It uses the Decimal.js library for precise arithmetic, avoiding the floating-point errors that can plague basic JavaScript math.

The display shows two lines: the expression you've built (like "15 + 23 × 2") and the current number or result. After pressing equals, the full expression with its result appears (like "15 + 23 × 2 = 61").

Button styling uses gradients and shadows for visual feedback. Number buttons have a light style; operator buttons have a darker style; equals stands out in amber; clear buttons appear in red.

All processing happens locally in your browser. No data is sent anywhere.

FAQs

Why does 5 + 3 × 2 give 11 instead of 16?

The calculator follows standard mathematical order of operations (PEMDAS/BODMAS). Multiplication happens before addition. So 3 × 2 = 6, then 5 + 6 = 11. If you want addition first, you'd need to calculate 5 + 3 separately, then multiply the result by 2.

What's the difference between C and CE?

C (Clear) resets the entire calculator—your expression, result, and any intermediate state. CE (Clear Entry) erases only the number you're currently entering, leaving the rest of your expression intact. CE is for fixing typos; C is for starting over.

Can I use my keyboard?

Yes. Number keys (0-9), decimal point (.), plus (+), minus (-), asterisk (*) for multiply, slash (/) for divide, and Enter for equals all work. Backspace deletes the last character.

Why do some calculations show many decimal places?

The calculator shows the precise result. For practical use, you'd round to an appropriate number of decimal places. Money typically uses 2 decimal places; other contexts might use more or fewer.

What happens if I divide by zero?

Division by zero is undefined in mathematics. The calculator will display an error or infinity indication rather than a numeric result.

Is there a limit to how large numbers can be?

Practically speaking, the calculator handles numbers far larger than you'd encounter in everyday calculations. You might hit display limits before mathematical ones.

Can I calculate percentages?

Yes, by converting the percentage to a decimal. To find 20% of a number, multiply by 0.20. To add 20% to a number, multiply by 1.20. To subtract 20%, multiply by 0.80.

Why can't I enter parentheses?

This is a basic calculator focused on simple arithmetic. For expressions requiring parentheses, you'd either calculate parts separately and combine results, or use a scientific calculator that supports parenthetical grouping.

How do I calculate a running total?

After each calculation, the result becomes your new starting point. For example, after 15 + 20 = 35, you can type + 10 = to get 45, then - 5 = to get 40. The calculator chains operations naturally.

What precision does the calculator use?

The calculator uses the Decimal.js library for arbitrary-precision arithmetic, avoiding the floating-point errors that can plague standard JavaScript math. For typical calculations, you'll see results accurate to many decimal places.

Can I use this calculator on mobile devices?

Yes. The interface is responsive and works on smartphones and tablets. The button grid adapts to screen size, and touch input works the same as mouse clicks.