How do I find X% of a number?

Select the 'X% of N' mode, enter the percent and the number, then click Calculate. The tool multiplies N by X/100.

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

Choose 'What percent is A of B?'. Enter A (part) and B (whole). The tool computes A/B × 100.

How do I increase or decrease by a percent?

Select 'Increase/Decrease by %', enter the base value and percent, choose Increase or Decrease, and hit Calculate.

📊 Percentage Calculator How to Calculate Percentages, Percent Change & Practical Examples

A friendly, step-by-step guide to understanding and calculating percentages. Learn how to compute X% of Y, determine what percent A is of B, and measure percentage increase or decrease with simple formulas and real-world examples.

🔎 What Is a Percentage?

A percentage expresses a number as a fraction of 100 and uses the percent sign %. It simplifies comparisons and shows proportions clearly: when you say “25%,” you mean 25 parts out of 100.

🧮 Common Percentage Calculations

1. Calculate X% of Y (part of a whole)

Formula: Part = (X / 100) × Y

Example: What is 15% of 200?
Part = (15 / 100) × 200 = 0.15 × 200 = 30. So, 15% of 200 is 30.

2. What percent is A of B?

Formula: Percent = (A / B) × 100

Example: If a test score is 18 out of 24:
Percent = (18 / 24) × 100 = 0.75 × 100 = 75%. The score is 75%.

3. Percentage change (increase or decrease)

Formula: Percentage change = ((New − Old) / |Old|) × 100

Example (increase): Price rises from 50 to 60.
Change = ((60 − 50) / 50) × 100 = 20% increase.
Example (decrease): Price drops from 80 to 56.
Change = ((56 − 80) / 80) × 100 = −30% → 30% decrease.

✅ Quick Reference: Formulas

Part from percent: Part = (Percent / 100) × Total
Percent of total: Percent = (Part / Total) × 100
Percent change: ((New − Old) / |Old|) × 100

📚 Practical Uses

Percentages are used in many everyday scenarios:

💳 Finance: interest, discounts, tax calculations.
📊 Data & analytics: conversion rates, growth percentages.
🏷️ Shopping: sale prices and “save X%” labels.
🎓 Education: exam scores and grade percentages.

🛠️ Tips & Common Pitfalls

Always identify the correct base value before calculating a percentage.
For percentage change, divide by the original (old) number — not the new one.
Avoid dividing by zero: if the original value is 0, percentage change is undefined; use absolute difference or clarify the context.
Round sensibly: two decimal places are usually sufficient for display.

📌 Example Scenarios

Discount: A jacket priced at $120 has a 25% discount. Discount amount = 0.25 × 120 = $30 → Sale price = $90.

Grade: Score 42 out of 50 → Percent = (42 / 50) × 100 = 84%.

Growth: Monthly users grow from 2,000 to 2,600. Change = ((2600 − 2000) / 2000) × 100 = 30% growth.

🔁 Handy Shortcuts

10% of a number → move the decimal one place left (e.g., 10% of 450 → 45).
5% → half of 10% (e.g., 5% of 450 → 22.5).
1% → move the decimal two places left (e.g., 1% of 450 → 4.5).

Percentage Calculator How to Calculate Percentages, Percent Change & Practical Examples