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Percentage Calculator

Work out percentages three ways: X% of Y, X as a % of Y, and percentage increase or decrease.

Updated

What is the Percentage Calculator?

The Percentage Calculator covers the three most common percentage calculations in one place.

Features

You can switch between three modes:

  • Calculate a percentage of a number
  • Find what percentage one number is of another
  • Measure percentage increase or decrease between two values

How It Works

  • Enter your values and results update instantly as you type
  • No need for a calculate button
  • Designed to avoid unexpected rounding errors

Use Cases

  • Quick math for shopping discounts
  • Comparing values in reports or data
  • Tracking growth or decline over time
  • Everyday financial and academic calculations

How it works

Each mode uses a standard percentage formula to ensure accurate and consistent results.

Formulas Used

  • X% of Y
    Multiply Y by X ÷ 100
    [ (Y \times X) / 100 ]

  • X is what % of Y
    Divide X by Y, then multiply by 100
    [ (X / Y) \times 100 ]

  • Increase / Decrease Percentage
    Calculate the change between two values, then divide by the original value and multiply by 100
    [ ((new - original) / original) \times 100 ]

  • Positive result = growth

  • Negative result = decrease

Accuracy & Safety

  • Prevents division by zero errors
  • Automatically trims unnecessary trailing decimals for cleaner output
  • Ensures consistent, readable results across all calculations

Examples

20% of 150

A 20% tip on a $150 bill.

Mode: X% of Y → X = 20, Y = 150
30

45 is what % of 60

Scoring 45 out of 60 on a test.

Mode: X is what % of Y → X = 45, Y = 60
75%

Price rise from 80 to 100

A product that went from 80to80 to100.

Mode: Increase / decrease → From = 80, To = 100
+25%

Frequently asked questions

How do I calculate a percentage of a number?

Use the “X% of Y” mode to calculate a percentage of any value. The calculation works as follows:

  • Multiply the number (Y) by the percentage (X) divided by 100.
  • Formula: (X ÷ 100) × Y
  • Example: 20% of 150 = (20 ÷ 100) × 150
  • Result: 30

How do I find what percentage one number is of another?

Use the “X is what % of Y” mode. Steps:

  • Divide the first number by the second number.
  • Multiply the result by 100.
  • Formula: (X ÷ Y) × 100
  • Example: 45 out of 60 = (45 ÷ 60) × 100
  • Result: 75%

How is percentage increase or decrease calculated?

Percentage change measures how much a value has increased or decreased relative to its original value. The process is:

  • Subtract the original value from the new value.
  • Divide the result by the original value.
  • Multiply by 100. Formula: ((New - Original) ÷ Original) × 100
  • A positive result indicates an increase.
  • A negative result indicates a decrease.

Why do I get an error when one value is zero?

Some percentage calculations require division by a non-zero number.

  • Division by zero is mathematically undefined.
  • A valid percentage cannot be computed when the denominator is zero.
  • Returning a result in such cases would be misleading or incorrect. For this reason, the calculator shows an error instead of producing an invalid or infinite value.

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