Guides

Percentage Calculation Guide

Percentages depend on the base value. Choose the base first, then interpret the result.

A percentage describes one number relative to another. Before calculating, ask which value is the base. A 20% result means different things when the base is original price, current price, revenue or cost.

Discounts usually use the decreased value. If the original price is 500 and the discount is 20%, the reduction is 100 and the new price is 400. The percent is based on the original price.

Growth and decline compare change. Going from 80 to 100 is a 25% increase, while going from 100 to 80 is a 20% decrease. The directions are related, but the bases are different.

Share describes part of a whole. If one expense is 150 and total expense is 1000, its share is 15%. Share is about structure, not movement.

Taxes, margins, investing and loans may involve periods, compounding, tiered rules or rounding. Use the tool for basic checking and confirm formal rules when needed.

Using the Guide with Tools

After reading a guide, open the related tool at the bottom of the page and replace the examples with your own numbers. Keep the input conditions, such as amount, date, unit, rate, height or weight, so the result can be reviewed later.

Reviewing Results

If a result affects payment, contracts, health decisions or formal planning, do not rely on a single online calculation. Use this site for an initial estimate, then confirm with source material, official quotes, professional documents or qualified advice.

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