How to Calculate Percentages Easily (With Examples)

Percentages are parts of 100. To find X% of a number, multiply by X and divide by 100: 20% of 150 is 30. To find what percent one number is of another, divide and multiply by 100: 45 out of 60 is 75%. For change, use (new − old) ÷ old × 100. The Percentage Calculator handles all four common questions and shows the working.

What is X% of Y?

Formula: Y × X ÷ 100

• 20% of 150 = 150 × 20 ÷ 100 = 30
• 15% tip on a $48 bill = 48 × 0.15 = $7.20
• 18% GST on Rs 2,500 = 2,500 × 0.18 = Rs 450

Quick mental trick: 10% is the number with the decimal moved one place left. 10% of 150 is 15, so 20% is 30 and 5% is 7.5.

X is what percent of Y?

Formula: X ÷ Y × 100

• 45 marks out of 60 = 45 ÷ 60 × 100 = 75%
• 380 out of 500 in an exam = 76%
• You saved 300 of a 1,200 target = 25%

This is the one to use for test scores, attendance and progress towards a goal.

What is the percentage change from X to Y?

Formula: (Y − X) ÷ X × 100

• Price from 80 to 100: (100 − 80) ÷ 80 × 100 = +25%
• Weight from 90 kg to 85.5 kg: (85.5 − 90) ÷ 90 × 100 = −5%
• Rent from 1,000 to 1,150: +15%

A negative result is a decrease. Always divide by the starting value, not the new one.

How do I increase or decrease a number by a percentage?

Increase: Y × (1 + X ÷ 100). Decrease: Y × (1 − X ÷ 100).

• $50 with 15% off: 50 × 0.85 = $42.50
• A salary of 60,000 with a 10% raise: 60,000 × 1.1 = 66,000
• Add 20% VAT to £100: 100 × 1.2 = £120

For tax specifically, the VAT & GST Calculator also removes tax from a price correctly (divide by 1.2, don't subtract 20%).

How do I use the percentage calculator?

The Percentage Calculator has four modes, matching the questions above:

1. What is X% of Y?
2. X is what % of Y?
3. % change from X to Y
4. Increase or decrease Y by X%

Choose the mode, type X and Y, and the answer appears as you type, with the working shown so you can check it.

Percentage points vs percent

If an interest rate goes from 4% to 5%, it rose by 1 percentage point, but by 25 percent (because 1 is 25% of 4). News reports mix these up often; percentage points are for differences between two percentages.

Common percentage mistakes

• Reversing a change. A 20% discount followed by a 20% increase doesn't return to the original price: 100 → 80 → 96.
• Dividing by the wrong number in percentage change. Use the starting value.
• Adding percentages of different totals. 50% of one class and 50% of another isn't "100%".
• Removing tax by subtracting. £120 including 20% VAT is £100 before tax, not £96.

Where you'll use percentages

• School: marks, grades and what you need on a final. See what you need on your final exam.
• Shopping: discounts and sale prices.
• Business: profit margins and markups, with the Profit Margin Calculator.
• Money: interest and savings growth, with the Compound Interest calculator.

Try it

Open the free Percentage Calculator, pick the question you're asking and enter the numbers. It works on any device and runs in your browser.