Guides
Percentage guides
Short, practical explanations of the percentage questions people run into while shopping, eating out, running a small business, reading the news, or saving money. Each guide shows the formula, a worked example, and the mistakes to avoid.
- Discounts and sales taxCalculate savings, sale prices, and tax in the right order.
- Tipping around the worldUnderstand common customs before calculating a tip.
- Common percentage mistakesSpot the errors that can make an answer misleading.
- Markup vs marginPrice products correctly and see why 50% markup is not 50% margin.
- Percent vs percentage pointsRead interest rates, polls, and statistics without being misled.
- Investment returns and compoundingWhy a 50% loss needs a 100% gain, and how growth really adds up.
- How to calculate a pay raiseWork out your raise percentage and what it really adds after inflation and tax.
- How credit card APR worksTurn an APR into daily interest and see what carrying a balance costs.
- How weighted grades workCalculate a final grade and the score you need on the final exam.
- How inflation affects purchasing powerSee what your money will buy after 5, 10, and 20 years of rising prices.
- Compound vs simple interest and the Rule of 72Estimate how long money takes to double with one quick division.
How to use these guides
Every guide is written to be read in a few minutes. Start with the formula, follow the worked example with your own numbers, then check the section on common mistakes. When you just need the answer, the percentage calculator does the arithmetic instantly in your browser.
The examples use round numbers and US dollars to keep the arithmetic easy to follow. The same methods work in any currency. Rules for tax, tipping, and investing vary by place and personal situation, so treat these guides as general explanations rather than financial, tax, or legal advice.