How to Calculate Percentage — 3 Types with Examples

Introduction

Percentage calculations are used everywhere — from exam scores and shopping discounts to salary hikes and GST computation. Despite being taught early in school, many students and professionals make errors because there are three different types of percentage problems, each requiring a slightly different formula.

This guide covers all three types with clear formulas, step-by-step examples, and tips to avoid common mistakes.

What is Percentage?

“Percent” means “per hundred.” A percentage expresses a number as a fraction of 100. The symbol % represents division by 100.

25% = 25/100 = 0.25

Type 1: Find X% of a Number

Question format: “What is 15% of 2400?”

Formula

Result = (Percentage / 100) × Number

Examples

What is 18% of ₹5,000? = (18/100) × 5000 = 0.18 × 5000 = ₹900

What is 7.5% of 12,000? = (7.5/100) × 12000 = ₹900

What is 33.33% of 600? = (33.33/100) × 600 = ₹200

Real-world uses:

• Calculating GST amount on a product
• Finding tip amount at a restaurant
• Computing salary increment
• Determining discount value

Type 2: What Percent is A of B?

Question format: “42 is what percent of 50?”

Formula

Percentage = (Part / Whole) × 100

Examples

42 out of 50 = ?% = (42/50) × 100 = 84%

350 out of 500 = ?% = (350/500) × 100 = 70%

18 out of 24 = ?% = (18/24) × 100 = 75%

Real-world uses:

• Calculating exam score percentage
• Finding attendance percentage
• Determining what fraction of budget was spent
• Comparing marks across different subjects with different totals

Type 3: Percentage Change (Increase or Decrease)

Question format: “Price went from ₹800 to ₹920. What is the percent increase?”

Formula

Percent Change = ((New Value − Old Value) / Old Value) × 100

• Positive result = increase
• Negative result = decrease

Examples

Price: ₹800 → ₹920 = ((920 − 800) / 800) × 100 = (120/800) × 100 = 15% increase

Salary: ₹45,000 → ₹40,500 = ((40,500 − 45,000) / 45,000) × 100 = (−4,500/45,000) × 100 = 10% decrease

Stock: ₹150 → ₹195 = ((195 − 150) / 150) × 100 = (45/150) × 100 = 30% increase

Real-world uses:

• Comparing year-over-year sales growth
• Measuring inflation or price rise
• Tracking weight loss/gain percentage
• Evaluating investment returns

Common Mistakes to Avoid

1. Dividing by the new value instead of old in percent change — always divide by the original (old) value
2. Adding percentages directly — 10% increase followed by 10% decrease does NOT return to the original (you get 99% of original)
3. Confusing “percentage” with “percentage points” — Interest rate going from 8% to 10% is a 2 percentage point increase but a 25% relative increase
4. Forgetting to multiply by 100 — This gives a decimal (0.15) instead of a percentage (15%)
5. Using wrong base — “A is what % more than B” means divide by B, not by A

Quick Mental Math Tips

• 10% of any number: Move decimal one place left (10% of 450 = 45)
• 5%: Find 10% and halve it (5% of 450 = 22.5)
• 25%: Divide by 4 (25% of 800 = 200)
• 1%: Move decimal two places left (1% of 3500 = 35)
• Combine: 15% = 10% + 5% (15% of 200 = 20 + 10 = 30)

Try It Online

Use the free Percentage Calculator on Numverto to solve all three types instantly. The tool shows the formula with your substituted values so you can learn while calculating. No signup required.

Frequently Asked Questions

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

Divide the part by the whole and multiply by 100. For example, 75 out of 300 = (75/300) × 100 = 25%.

What is the formula for percentage increase?

Percentage increase = ((New − Old) / Old) × 100. Always divide by the original (old) value, not the new value.

Can a percentage be more than 100%?

Yes. If a number doubles, the increase is 100%. If it triples, the increase is 200%. Values above 100% simply mean the result exceeds the base reference.

How do I convert a decimal to percentage?

Multiply by 100. For example, 0.85 = 85%, 1.5 = 150%, 0.07 = 7%.

What is the difference between percent and percentage points?

If an interest rate changes from 5% to 8%, it increased by 3 percentage points. But the relative percent increase is (3/5)×100 = 60%. “Percentage points” is an absolute difference; “percent change” is relative.