What is order of operations (BODMAS/PEMDAS)?

Order of operations determines which calculations are performed first in an expression. BODMAS: Brackets, Orders (powers/roots), Division, Multiplication, Addition, Subtraction. PEMDAS (US): Parentheses, Exponents, Multiplication, Division, Addition, Subtraction. Both mean the same thing: brackets/parentheses first, then powers, then multiply/divide left-to-right, then add/subtract left-to-right.

How do I calculate a percentage on a calculator?

To find 15% of 200: type 200 × 15 ÷ 100 = (result: 30). Or on calculators with a % button: type 200 × 15% = (same result). To add 15% to 200: type 200 × 1.15 = (result: 230). To subtract 15%: type 200 × 0.85 = (result: 170).

Why does 0.1 + 0.2 not equal 0.3 on computers?

0.1 + 0.2 equals 0.30000000000000004 in most programming languages because computers store numbers in binary floating-point format, and 0.1 cannot be represented exactly in binary (just as 1/3 cannot be represented exactly in decimal). This is an inherent limitation of IEEE 754 floating-point arithmetic, not a bug. For most everyday calculations, the difference is negligible.

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A full-featured online calculator with calculation history. Add, subtract, multiply, divide, use brackets for complex expressions, and review your previous calculations.

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How to Use This Calculator

Click the buttons or use your keyboard to enter calculations. The display shows your current input; the expression line shows the full equation being built. Press AC to clear everything, or use the backspace key to delete the last character.

Keyboard shortcuts: 0–9 for digits, + − * / for operations, Enter or = for result, Backspace to delete, Escape to clear all, % for percentage.

Clicking a previous result in the history panel loads it back into the calculator so you can continue from that value.

Order of Operations — BODMAS / PEMDAS

When a calculation contains multiple operations, they are performed in a specific order — not simply left to right. This order is called BODMAS (UK/Australia) or PEMDAS (US):

Letter	BODMAS	PEMDAS	Example
B / P	Brackets	Parentheses	(2 + 3) × 4 = 20, not 14
O / E	Orders (powers)	Exponents	2² before × or +
D / M	Division	Multiplication	Performed left to right
M / D	Multiplication	Division	Same level as above
A / A	Addition	Addition	Performed left to right
S / S	Subtraction	Subtraction	Same level as above

Example: 10 + 2 × 6 = 10 + 12 = 22 (not 72, because multiplication before addition). With brackets: (10 + 2) × 6 = 12 × 6 = 72.

Common Calculation Types and Formulas

Percentages on a calculator

X% of Y: type Y × X ÷ 100 =
Add X% to Y: type Y × (1 + X÷100) = or Y + (Y × X ÷ 100) =
Subtract X%: type Y × (1 − X÷100) =
What % is X of Y: type X ÷ Y × 100 =

Area and volume calculations

Rectangle area: length × width
Circle area: 3.14159 × radius × radius
Cylinder volume: 3.14159 × radius² × height
Triangle area: 0.5 × base × height

Financial calculations

Simple interest: Principal × Rate × Time
Percentage increase: ((New − Old) ÷ Old) × 100
Splitting a bill: Total ÷ number of people
Tip amount: Bill × tip percentage ÷ 100

Mental Maths Strategies for Everyday Calculations

A calculator is always faster, but understanding mental maths strategies helps you estimate quickly and catch errors before they cost you money. The most useful techniques:

Rounding and compensation

Round numbers to make calculations easier, then adjust. £19.99 × 3 = round to £20 × 3 = £60, minus 3p = £59.97. 47 + 38: round to 50 + 40 = 90, minus 3 + 2 = 85. This technique works for any addition or multiplication where rounding simplifies one factor.

Breaking apart numbers

Decompose numbers into familiar parts. 13 × 7: break into (10 × 7) + (3 × 7) = 70 + 21 = 91. 136 + 47: add tens first (130 + 40 = 170), then units (6 + 7 = 13), total = 183. This left-to-right method (unlike the right-to-left written method taught in school) is faster for mental calculation because the big, important digits are handled first.

Multiplying by 5, 25, 50, 99

×5: divide by 2 and multiply by 10. 46 × 5 = 46/2 × 10 = 230
×25: divide by 4 and multiply by 100. 32 × 25 = 32/4 × 100 = 800
×50: divide by 2 and multiply by 100. 18 × 50 = 18/2 × 100 = 900
×99: multiply by 100 and subtract the original. 47 × 99 = 4700 − 47 = 4653

Number Systems and Bases

Standard arithmetic uses base 10 (decimal) — digits 0–9, where position represents powers of 10. Computers use base 2 (binary) — only 0s and 1s. This is why a seemingly simple sum like 0.1 + 0.2 produces 0.30000000000000004 in most programming languages: the decimal fraction 0.1 cannot be represented exactly in binary floating-point format, just as 1/3 cannot be represented exactly in decimal. For everyday calculator use this doesn't matter — the error occurs in the 16th decimal place — but it's why financial software uses decimal arithmetic libraries rather than standard floating-point.

The History of Calculation

Before electronic calculators, complex arithmetic was performed using mechanical calculators (Pascaline, 1642), logarithm tables (1614), and the slide rule (1622). The first mass-market electronic calculator, the Busicom 141-PF, was released in 1970 using the Intel 4004 chip. Texas Instruments' Datamath in 1972 brought pocket calculators to consumers for $149 ($1,100 in today's money). By 1975, prices had fallen below $25. Today, the same arithmetic runs as JavaScript in a browser tab in milliseconds — the first calculator on a webpage.

Frequently Asked Questions

BODMAS/PEMDAS determines which operations run first: Brackets/Parentheses first, then powers, then multiplication and division (left to right), then addition and subtraction (left to right). Example: 10 + 2 × 6 = 22, not 72, because the multiplication runs before the addition.

To find 15% of 200: type 200 × 15 ÷ 100 = (answer: 30). To add 15% to 200: type 200 × 1.15 = (answer: 230). To subtract 15%: type 200 × 0.85 = (answer: 170).

0.1 + 0.2 = 0.30000000000000004 in binary floating-point arithmetic because 0.1 cannot be represented exactly in binary — just as 1/3 cannot be expressed exactly in decimal. This is an inherent limitation of how computers store decimal numbers, not a calculator bug. For everyday calculations, the difference is negligible.

Yes. Use number keys (0–9), + − * / for operations, Enter or = for result, Backspace to delete, and Escape to clear. This is often faster than clicking buttons for complex calculations.