Free Percentage Calculator — Increase, Decrease & Difference

How to Use a Percentage Calculator: Quick Guide for BeginnersA percentage calculator is a simple tool that helps you compute percentages quickly and accurately without doing the manual arithmetic. Whether you’re figuring out discounts, tips, interest rates, or grade percentages, a percentage calculator saves time and reduces mistakes. This guide explains the common percentage tasks, how to use a calculator for each, and gives clear examples so you can practice.

What is a percentage?

A percentage expresses a number as a part of 100. For example, 25% means 25 out of 100. Percentages let you compare quantities of different sizes on the same scale.

Basic percentage operations and how to calculate them

1. Converting a percentage to a decimal

   • Method: divide the percentage by 100.
   • Example: 15% → 15 ÷ 100 = 0.15.
   • Use in calculator: enter 15 ÷ 100 = 0.15.

2. Converting a decimal to a percentage

   • Method: multiply the decimal by 100.
   • Example: 0.32 × 100 = 32%.
   • Use in calculator: enter 0.32 × 100 = 32.

3. Finding a percentage of a number (X% of Y)

   • Method: (X ÷ 100) × Y.
   • Example: 20% of 150 = (20 ÷ 100) × 150 = 0.2 × 150 = 30.
   • Calculator steps: enter 20 ÷ 100 × 150 = 30.

4. Calculating what percentage one number is of another (X is what % of Y)

   • Method: (X ÷ Y) × 100.
   • Example: 30 is what percent of 200 = (30 ÷ 200) × 100 = 0.15 × 100 = 15%.
   • Calculator steps: enter 30 ÷ 200 × 100 = 15.

5. Finding the amount after percentage increase/decrease

   • Increase method: Y × (1 + X ÷ 100).
   • Decrease method: Y × (1 − X ÷ 100).
   • Examples:
     • Increase: 150 increased by 10% → 150 × 1.10 = 165.
     • Decrease: 150 decreased by 10% → 150 × 0.90 = 135.
   • Calculator steps: enter 150 × (1 + 10 ÷ 100) = 165 or 150 × (1 − 10 ÷ 100) = 135.

6. Finding the percentage change between two numbers

   • Method: ((New − Old) ÷ Old) × 100.
   • Example: Price from 80 to 100 → ((100 − 80) ÷ 80) × 100 = (20 ÷ 80) × 100 = 25%.
   • Calculator steps: enter (100 − 80) ÷ 80 × 100 = 25.

Using an online percentage calculator

Most online percentage calculators have labeled fields for the types above: “Calculate X% of Y,” “What percent is X of Y,” “Increase/decrease by %,” and “Percentage change.” Steps are always:

• Choose the operation.
• Enter the numbers into the labeled fields.
• Click “Calculate” or the equivalent button. Results are shown instantly, often with a short explanation.

Practical examples and use cases

• Shopping discounts: If a pair of shoes costs \(120 with 25% off, calculate 25% of 120 = 30, then 120 − 30 = \)90.
• Tips at a restaurant: For a 18% tip on a \(45 bill → 45 × 0.18 = \)8.10, total = $53.10.
• Grades: If you scored 42 out of 50, percent = (42 ÷ 50) × 100 = 84%.
• Finance: To find monthly interest percentages or percent change in investments, use the percentage change formula above.

Tips to avoid mistakes

• Remember to convert percentages to decimals when multiplying (divide by 100).
• For increase/decrease, use 1 ± (percentage ÷ 100) to get the final amount directly.
• Watch the order of operations in calculators — use parentheses when needed.
• Double-check whether a percentage is relative to the original amount or the new amount.

Quick reference formulas

• Percentage to decimal: p% = p ÷ 100
• Decimal to percentage: d = d × 100%
• X% of Y: Y × (X ÷ 100)
• X is what % of Y: (X ÷ Y) × 100
• Increase by X%: Y × (1 + X ÷ 100)
• Decrease by X%: Y × (1 − X ÷ 100)
• Percentage change: ((New − Old) ÷ Old) × 100

If you want, I can add interactive examples, printable cheat-sheet, or step-by-step practice problems with solutions.