How to Calculate Percentage - A Simple Guide

Percentages are everywhere, on your payslip, at the checkout, in your exam results, and in the news. Yet many people still reach for their phone to work them out, unsure of the steps. This guide explains exactly how percentage calculations work, with clear formulas and everyday examples you can apply immediately. By the end, you'll be able to calculate any percentage confidently, and for the times when you want an instant answer, our free calculator is right here.

What is a Percentage?

A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin per centum, meaning "out of one hundred". When you see 75%, it simply means 75 out of every 100.

Percentages are useful because they create a common scale. Whether you're comparing a test score, a discount, or a tax rate, expressing values as percentages makes them easier to understand and compare.

The Core Percentage Formula

The formula you'll use most often is:

This answers the question: "What percentage is this number out of that number?"

Example

You scored 36 out of 45 on a test. What was your percentage?

1. Divide the part by the whole: 36 ÷ 45 = 0.8
2. Multiply by 100: 0.8 × 100 = 80
3. Result: 80%

How to Find a Percentage of a Number

This is the other common calculation: "What is X% of Y?"

Example

What is 15% of $240?

1. Divide the percentage by 100: 15 ÷ 100 = 0.15
2. Multiply by the number: 0.15 × 240 = 36
3. Result: $36

This comes up constantly when calculating discounts, tips, and commissions.

How to Calculate Percentage Increase and Decrease

When a value changes, you often need to know by what percentage it went up or down:

A positive result means an increase; a negative result means a decrease.

Example

A product's price rose from $80 to $100.

1. Subtract old from new: 100 − 80 = 20
2. Divide by old value: 20 ÷ 80 = 0.25
3. Multiply by 100: 0.25 × 100 = 25%
4. Result: A 25% increase

Reverse Percentage: Working Backwards from a Total

Sometimes you know the final amount and need to find the original. For example, if a price includes 10% tax and you want the pre-tax figure:

Example

A product costs $110 including 10% tax. What is the original price?

1. 110 ÷ 1.10 = $100
2. Result: The original price was $100

Quick Mental Percentage Shortcuts

These shortcuts let you estimate percentages in your head quickly:

• 10%: divide the number by 10 → 10% of $350 = $35
• 5%: find 10%, then halve it → 5% of $350 = $17.50
• 25%: divide the number by 4 → 25% of $200 = $50
• 50%: divide the number by 2 → 50% of $90 = $45
• 1%: divide the number by 100 → 1% of $640 = $6.40

For any two of these combined, say 15%, find 10% and 5% separately, then add them together.

Real-Life Percentage Examples

Discounts While Shopping

A $180 jacket is 30% off. Final price = $180 × (1 − 0.30) = $180 × 0.70 = $126.

Pay Rise Calculation

You earn $58,000 and get a 4% raise. Increase = $58,000 × 0.04 = $2,320. New salary = $60,320.

GST or Tax Calculation

Adding 10% GST to $450: $450 × 1.10 = $495. Removing 10% GST from $495: $495 ÷ 1.10 = $450.

Common Percentage Mistakes to Avoid

• Confusing "percentage of" with "percentage change" because they use different formulas.
• Forgetting to divide by 100 before multiplying.
• Using the wrong base value in a percentage change calculation.
• Assuming 20% off then 20% on gets you back to the original value. It doesn't; you end up at 96%.

Related Reading

Before you go, these posts will help you put today's topic into practice:

• How to split a bill with friends (and calculate tip) – put percentage maths to work in real life.
• Basic maths formulas every adult should know – a complete reference for everyday calculations.
• 5 everyday situations where a calculator saves you money – see where these skills make the biggest difference.

Final Thoughts

Percentages don't have to feel complicated. Once you know the three core formulas, finding a percentage, working out an amount, and calculating change, you'll handle them confidently in any situation. Keep this guide bookmarked as a quick reference whenever you need it.