What a percentage really means
A percentage is a way of writing a part of a whole as “per hundred.” If something is 25%, it is 25 parts out of every 100 parts. That idea covers exam scores, discounts, growth rates, and tip amounts.
The three formulas you need most
Most everyday percentage questions fall into one of these patterns.
1. Find a percentage of a number
Part = (Percentage ÷ 100) × Whole
Example: What is 18% of 250?
(18 ÷ 100) × 250 = 45
2. Convert a score into a percentage
Percentage = (Part ÷ Whole) × 100
Example: You scored 72 out of 90.
(72 ÷ 90) × 100 = 80%
3. Calculate percentage change
Percentage change = ((New − Old) ÷ Old) × 100
Example: A price rises from 400 to 460.
((460 − 400) ÷ 400) × 100 = 15% increase
If the result is negative, the value decreased.
Common mistakes to avoid
- Using the wrong “whole.” A 20% discount on 1,000 is based on 1,000, not on the discounted price.
- Adding percentages that apply to different bases (for example, stacking successive discounts incorrectly).
- Confusing percentage points with percent change. Moving from 10% to 12% is a 2 percentage-point rise, but a 20% relative increase.
Quick real-life uses
- Shopping: Find the discount amount and final price.
- School: Convert marks into percentages and compare subjects.
- Business: Track growth, margins, and conversion rates.
Want the answer without the arithmetic? Use the free Percentage Calculator. For shopping math, try the Discount Calculator.