Math &amp; money

Percentage Calculator

Work out percentages, increase, decrease and the difference between two numbers instantly, with a chart.

ROI Calculator

Calculate return on investment, net profit and the annualised return for any project.

VAT Calculator

Add VAT to an amount or extract it from a VAT-inclusive price at any rate, with a full breakdown.

Discount Calculator

Find the sale price and your saving, and work out stacked discounts correctly.

Unit Converter

Convert length, weight, temperature, area and volume units instantly.

Proportion Calculator

Solve proportions and find a missing value.

Ratio Calculator

Simplify ratios and divide quantities.

Average Calculator

Calculate mean, sum and range.

Markup Calculator

Calculate selling price, profit and margin.

Tip Calculator

Calculate the right tip and split the bill automatically among everyone at the table.

Random Number Generator

Generate one or several truly random numbers between any two values, with an optional no-repeat mode.

Articles & guides

Sampling Without Replacement: 5 Practical Examples

Five practical examples explain no-repeat number selection, changing probabilities and how to prevent duplicate selections across separate batches.

How to Average Percentages: 5 Worked Examples

Five practical examples explain when a simple average of percentages works, when to weight the rates, and how to calculate…

Markup vs Margin: 5 Pricing Examples to Avoid Mix-Ups

Compare markup vs margin through 5 worked pricing examples. Learn both formulas, convert a margin target and check the result…

Ratio vs Fraction: 5 Examples That Make the Difference Clear

Understand ratio vs fraction with 5 worked examples. Compare parts, divide totals, simplify ratios and calculate percentage shares with our…

Stacked Discounts: 5 Examples to Calculate the Real Saving

Calculate stacked discounts with 5 worked examples. Learn why 20% off plus another 10% saves 28%, and check each step…

Percentage Difference vs Percentage Change: Formulas and Examples

Learn percentage difference vs percentage change with formulas, price and sales examples, percentage points, and common calculation mistakes.

How to Calculate Percentage Decrease: Formula and Examples

Percentage decrease shows how much a value has fallen relative to its original amount. It is useful for price reductions,…

How to Reverse a Percentage and Find the Original Number

A reverse percentage calculation finds the original number before a percentage was added, removed, or applied. The key is to…

How to Calculate Percentage Error: Formula and Examples

Percentage error measures how far an observed or experimental value is from an accepted value. It expresses the difference as…

How to Convert Kilograms, Pounds, Celsius, and Fahrenheit

Conversions between kilograms and pounds are common in shopping, shipping, and fitness, while Celsius and Fahrenheit appear in travel, cooking,…

How to Convert Length, Area, and Volume Units Correctly

Length, area, and volume units appear in property listings, screen sizes, furniture specifications, land records, and tank capacities. Errors occur…

Complete Guide to Unit Conversion with Examples

Unit conversion appears in recipes, product dimensions, travel distances, shipping weights, and technical work. One incorrect factor can produce an…