Percentage Calculator: How to Calculate Any Percentage

The Four Core Percentage Calculations

How to Use the Percentage Calculator

1. Open the Percentage Calculator.
2. Select a calculation mode from the four buttons at the top.
3. Enter your values — the labels tell you exactly what each field expects.
4. The result and formula appear instantly. No button to press.

Percentage Formulas Explained

Finding X% of a number

This is the most common percentage calculation. To find 15% of 200, divide 15 by 100 to get 0.15, then multiply by 200: 0.15 × 200 = 30. This is the calculation behind tip amounts, discounts, and commission payments.

What percent is X of Y?

Divide X by Y and multiply by 100. To find what percentage 45 is of 180: (45 ÷ 180) × 100 = 25%. This is used for converting exam scores to percentages, calculating market share, and expressing a part as a proportion of a whole.

Percentage change

Percentage change measures how much a value changed relative to its starting point. Formula: ((New − Old) ÷ |Old|) × 100. If a stock goes from 80 to 100, the change is ((100 − 80) ÷ 80) × 100 = +25%. If it falls from 100 to 80, the change is ((80 − 100) ÷ 100) × 100 = −20%. Note that a 25% rise followed by a 20% fall returns to the original value — the asymmetry is important.

Increase or decrease by a percentage

To increase a value by X%, multiply by (1 + X/100). To decrease by X%, multiply by (1 − X/100). Adding 20% VAT to £50: 50 × 1.20 = £60. Applying a 30% discount to £60: 60 × 0.70 = £42.

Real-World Use Cases

Retail discounts

A product priced at £120 is on sale at 25% off. Use “Decrease by X%” — enter 25 and 120. Result: £90. The saving is £30, confirmed by “X% of Y”: 25% of 120 = 30.

Tax calculation

A freelancer earns $3,500 and pays 22% income tax. Use “X% of Y”: 22% of 3500 = $770 in tax, leaving $2,730. Or use “Decrease by X%” to get the net amount directly: 3500 reduced by 22% = $2,730.

Investment returns

A portfolio grows from $12,000 to $14,400 over a year. Use “Percentage change”: ((14400 − 12000) ÷ 12000) × 100 = +20%. That is the annual return.

Exam and test scores

A student scores 68 out of 85. Use “X is what % of Y”: (68 ÷ 85) × 100 = 80%. To check whether they passed a 70% threshold: 70% of 85 = 59.5, so 68 is a pass.

Common Percentage Mistakes

Percentage increases and decreases are not symmetric

Increasing a value by 50% and then decreasing by 50% does not return to the original. 100 + 50% = 150. 150 − 50% = 75. This asymmetry matters in finance — a 50% portfolio loss requires a 100% gain just to break even.

Percentage change vs. percentage points

If an interest rate rises from 4% to 5%, that is a 1 percentage point increase, but a 25% percentage change ((5 − 4) ÷ 4 × 100). These two phrases mean very different things and are frequently confused in financial reporting.