How to Work Out Percentage: Formula, Steps & Examples

Percentages are everywhere—from supermarket discounts to exam scores. If you’ve ever wondered whether a price cut actually saved you money, this guide cuts straight to it. You’ll find the core formula that works every time, mental shortcuts for calculating in your head, and step-by-step methods for calculators and spreadsheets.

Basic percentage formula: (part ÷ whole) × 100 · 20% of 80: 16 · 30% of 500: 150 · 5% of 300: 15 · 3/20 as percentage: 15% · 20% of 70: 14

These core formulas and shortcuts appear consistently across educational resources, from university guides to tech education platforms.

How do I calculate a percentage of an amount?

Percentage formula basics

The universal formula for any percentage calculation is (part ÷ whole) × 100, according to CalculatorSoup. This means you divide the smaller value by the larger value and multiply by 100 to get your answer. For example, to find what percentage 30 is of 50, you calculate (30 ÷ 50) × 100 = 60%. The formula remains the same whether you’re working with dollars, kilograms, or any other unit.

Step-by-step example

Let’s work through a practical example: what is 20% of 80? According to the Open University calculator guide, you can find 20% by first finding 1% (divide by 100), then multiplying by 20. So 1% of 80 is 0.8, and 0.8 × 20 = 16. Most calculators also have a dedicated % button that handles this automatically—type 80 × 20 % and you’ll get 16 directly.

What is the easiest way to calculate percentage?

Mental math techniques

The easiest mental approach breaks percentages into familiar fractions, as explained by GeeksforGeeks. This technique works because certain percentages correspond exactly to simple fractions: 50% equals one-half, 25% equals one-quarter, and 10% is one-tenth. To find 50% of 200, simply halve it to get 100. For 25% of 60, divide by 4 to get 15.

Using equivalent fractions

The 10% trick forms the foundation for most mental percentage calculations, according to StudyPug. To find 10% of any number, move the decimal point one place left. Once you have 10%, you can combine it with other percentages: 15% is 10% plus 5%, and 5% is simply half of 10%. For instance, 15% of 300 starts with 10% (30), adds 5% (15), to equal 45.

How do I take 20% off a price?

Discount calculation steps

To subtract a percentage from a price, first calculate the percentage of the original amount, then subtract it from the original, according to Calculator.net. A cleaner method is to multiply the original price by (1 – percentage/100). For a 20% discount on an £80 item: £80 × (1 – 20/100) = £80 × 0.8 = £64. You saved £16.

Real price examples

The Open University notes that most price calculators work by finding the percentage amount first, then subtracting it from the original total. If an item costs £50 and you want 20% off: calculate 20% of £50 (which is £10), then subtract: £50 – £10 = £40. The shortcut method—multiplying by 0.8—gives the same result in one step.

How to work out percentage increase?

Increase formula

Percentage increase follows a specific formula: ((new value – original value) ÷ original value) × 100, as detailed by CalculatorSoup. If a stock rises from £50 to £65, the increase is ((65 – 50) ÷ 50) × 100 = (15 ÷ 50) × 100 = 30%. The increase represents 30% of the original price.

Example walkthrough

GeeksforGeeks explains that percentage decrease uses a similar approach but with the new value as the denominator: ((original – new) ÷ original) × 100. If a product drops from £50 to £30, the decrease is ((50 – 30) ÷ 50) × 100 = 40%. The key difference is whether you’re comparing to the starting point or the ending point.

How to work out percentage on a calculator?

Calculator steps

The Open University’s mathematics guide confirms two reliable calculator methods for percentages. Method one: divide the number by 100 to find 1%, then multiply by the percentage you need. Method two: use the % button directly—type the number, press multiply, type the percentage, then press the % key. For example, 500 × 30 % gives you 150 instantly.

Excel percentage functions

For spreadsheet work, OmniCalculator recommends the formula =(A1/B1)*100 to calculate what percentage A1 is of B1. If cell A1 contains your part value and B1 contains your whole value, this formula gives you the percentage. According to the Open University’s Excel guide, you can then format the result as a percentage by selecting the cell and clicking the % format button.

How to work out percentage on Excel?

Excel formula basics

For calculating what percentage one number is of another in Excel, use =(A1/B1)*100, where A1 contains the part value and B1 contains the whole value, according to OmniCalculator. This formula divides the part by the whole and multiplies by 100 to produce the percentage value directly.

Formatting and common pitfalls

The Open University explains that Excel’s percentage format button multiplies the cell value by 100 for display purposes. If your formula already yields a decimal like 0.6 (representing 60%), applying percentage formatting will display 60%—but the underlying value remains 0.6, which matters when using the cell in further calculations.

Percentage calculation steps

Whether you’re working with mental math, a calculator, or Excel, the percentage calculation process follows a consistent pattern:

• Identify your values: Determine which number is the part (smaller value) and which is the whole (larger value you’re comparing to)
• Apply the formula: Divide part by whole, then multiply by 100
• Check your result: Verify by reversing the calculation—if you calculated 20% of 80 = 16, then 16 should be approximately 20% of 80
• Round if needed: For estimates, round numbers first to get a quick approximation before the exact calculation

“You can work out any percentage on a calculator by dividing by 100 first (to find 1%) and then multiplying the amount by the percentage you need.”

— Open University (Higher Education Institution)

“Splitting Percentages is a mental math technique that involves decomposing a percentage into smaller, more easily calculated parts.”

— GeeksforGeeks (Tech Education Platform)

For students calculating exam percentages, the formula helps convert raw marks into percentage scores. For shoppers evaluating discounts, the same principle applies in reverse—subtracting the percentage from the original price. For analysts tracking growth, percentage increase calculations reveal how values change relative to their starting point.

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Once comfortable with basic percentages, tackling the percentage increase formula becomes straightforward for scenarios like sales growth or price hikes.

Frequently asked questions