How to calculate percentage — step by step with examples

Percentage calculations are used in discounts, grades, finance, statistics, and everyday decisions. Learn the formulas and how to apply them.

What is a percentage

A percentage is a way to express a number as a fraction of 100. The symbol % means "per hundred." Percentages make it easy to compare proportions, track changes, and express ratios in a universal way that everyone understands regardless of the original scale.

The five most common percentage calculations

1. Find X% of a number

Formula: Result = (X ÷ 100) × Total

Example: What is 15% of 2400? → (15 ÷ 100) × 2400 = 360

2. Find what percentage X is of Y

Formula: Percentage = (X ÷ Y) × 100

Example: 45 out of 180 = (45 ÷ 180) × 100 = 25%

3. Calculate percentage change

Formula: Change % = ((New − Old) ÷ Old) × 100

Example: Price went from 800 to 960 → ((960 − 800) ÷ 800) × 100 = 20% increase

4. Increase a value by a percentage

Formula: Result = Value × (1 + Rate ÷ 100)

Example: 5000 increased by 18% GST → 5000 × 1.18 = 5900

5. Decrease a value by a percentage

Formula: Result = Value × (1 − Rate ÷ 100)

Example: 1200 after 25% discount → 1200 × 0.75 = 900

Quick percentage shortcuts

• 10% of any number: move the decimal one place left (10% of 450 = 45)
• 5% of any number: half of 10% (5% of 450 = 22.5)
• 1% of any number: move decimal two places left (1% of 450 = 4.5)

Use the Percentage Calculator on Smartweb.tools for instant calculations across all five modes.