Percentage Calculator Help

Quick Start

1

Choose a Calculator

Select the percentage calculation you want from the tabs at the top of the calculator.

2

Enter Your Numbers

Enter the values required for the calculation you selected.

3

Select Calculate

Press the Calculate button or press Enter on your keyboard.

4

Read the Result

The result is displayed together with a simple explanation of the formula used.

Tip: Percentage calculations can look similar but answer different questions. Choose the calculator that best matches what you are trying to find.

Percentage Calculators

What is X% of Y?

Use this calculator when you want to find a percentage of a number.

Example:
What is 15% of 250?

Result: 37.5

250 × 15 ÷ 100 = 37.5

X is what percentage of Y?

Use this when you know two numbers and want to find what percentage the first number is of the second.

Example:
50 is what percentage of 200?

Result: 25%

50 ÷ 200 × 100 = 25%

Percentage Change

Percentage Change shows how much a value has increased or decreased compared with its original value.

Example:
Original value: 80
New value: 100

Result: 25% increase

(100 − 80) ÷ 80 × 100 = 25%

Increase a Number by X%

Use this when you want to add a percentage to a starting value.

Example:
Increase 200 by 10%.

Result: 220

200 × 1.10 = 220

Decrease a Number by X%

Use this when you want to reduce a starting value by a percentage.

Example:
Decrease 200 by 10%.

Result: 180

200 × 0.90 = 180

Percentage Difference

Percentage Difference compares two values when neither value is specifically considered the original value. It uses the average of the two values as the reference.

Example:
Compare 80 and 100.

Difference = 20
Average = 90
Percentage difference = 22.22%

|80 − 100| ÷ ((80 + 100) ÷ 2) × 100

Find the Original Value Before an Increase

Use this calculator when you know the final value and the percentage increase, but want to find the original value.

Example:
Final value: 110
Increase: 10%

Original value: 100

110 ÷ 1.10 = 100

Find the Original Value Before a Decrease

Use this when you know a final value after a percentage reduction and want to find the original amount.

Example:
Final value: 90
Decrease: 10%

Original value: 100

90 ÷ 0.90 = 100

Percentage Change vs Percentage Difference

These two calculations are commonly confused.

When should I use Percentage Change?

Use Percentage Change when one value is clearly the original or starting value and the second value is the new value.

A price rises from $80 to $100.
The percentage increase is 25%.

When should I use Percentage Difference?

Use Percentage Difference when you are simply comparing two values and neither one is considered the starting value.

You are comparing two measurements from different sources and want to know how far apart they are as a percentage.

Common Uses

Discounts and Sale Prices

You can use the percentage decrease calculator to work out a discounted price.

$250 reduced by 20% = $200

Price Increases

Use Increase by Percentage to calculate a new price after a percentage rise.

$100 increased by 7.5% = $107.50

Test Scores

Use X is what percentage of Y to convert a score into a percentage.

42 marks out of 50 = 84%

Business and Financial Figures

Percentage calculations can be useful for comparing sales figures, costs, profit changes, budgets and other business values. For more specialised business calculations, you can also use the CS17 Business Calculator Workshop.

Frequently Asked Questions

Can I enter decimal percentages?

Yes. You can enter percentages such as 2.5%, 7.25% or 12.75%.

Can I enter negative numbers?

The calculator supports negative values where the calculation mathematically allows them. Keep in mind that negative values can change the meaning of a percentage comparison, particularly for percentage change.

Why can't Percentage Change start from zero?

Percentage Change divides the difference by the original value. Because division by zero is undefined, a conventional percentage change cannot be calculated when the original value is zero.

Can I calculate a 100% decrease backwards?

No. A 100% decrease reduces any starting value to zero. Once the final value is zero, the original amount cannot be determined from the percentage alone.

Are results rounded?

The calculator may round very long decimal results for easier reading. Internal calculations use the browser's normal numerical precision.

Can I use the Enter key?

Yes. After entering your values, press Enter to calculate the currently selected percentage calculation.

Does it work on mobile phones?

Yes. The CS17 Percentage Calculator is designed to work on desktop computers, laptops, tablets and mobile phones.

Do I need to create an account?

No. The Percentage Calculator can be used without creating an account or signing in.

Calculation Information

CS17 Percentage Calculator is designed as a general calculation tool. Results should be checked independently where accuracy is important.

Important: Percentage calculations can be affected by rounding, the meaning of the values being compared and the method used for a particular industry or application. For important financial, accounting, engineering, scientific or professional decisions, confirm the appropriate calculation method before relying on the result.

Need More Help?

If you find a problem with the calculator or have an idea for another percentage calculation, please contact us.

CS17 Tools
Email: admin@cs17.net