Percentage Calculator Guide 2025 – Formula & Examples

Introduction

Percentages are everywhere—discounts, tips, tax, and interest rates. Yet, "how to calculate percentage" remains one of the most searched math questions.

The Percentage Calculator solves three common problems:

1. What is X% of Y? (e.g., tip)
2. X is what percent of Y? (e.g., test score)
3. Percentage increase/decrease (e.g., raise or sale)

1. How to Calculate Percentage of a Number

Formula: (Percentage / 100) × Total Value

Example: What is 20% of ?

• Convert 20% to decimal: 0.20
• Multiply: 0.20 × 50 = 10
• Answer:

Real World Use: Tipping

• Bill:
• Tip: 15%
• Calc: 0.15 × 80 =

2. How to Find What Percent One Number is of Another

Formula: (Part / Whole) × 100

Example: You got 45 out of 50 on a test.

• Divide: 45 / 50 = 0.9
• Multiply by 100: 0.9 × 100 = 90%
• Answer: 90%

3. Percentage Increase & Decrease Formula

Formula: ((New Number - Original Number) / Original Number) × 100

Example (Increase): Rent went from ,000 to ,200.

• Difference: 1,200 - 1,000 = 200
• Divide by original: 200 / 1,000 = 0.2
• Multiply by 100: 20% increase

Example (Decrease): Shirt was , now .

• Difference: 30 - 50 = -20
• Divide by original: -20 / 50 = -0.4
• Multiply by 100: -40% decrease (or 40% off)

Common Percentage Shortcuts

• 10%: Move decimal one place left (.00 → .00)
• 20%: Find 10%, then double it
• 50%: Divide by 2
• 5%: Find 10%, then divide by 2
• 1%: Move decimal two places left (.00 → /bin/zsh.50)

FAQ

Q: How do I calculate a 20% discount? A: Multiply price by 0.8 (because you pay 80%).

• item × 0.8 = .

Q: How do I reverse a percentage? (Reverse Tax) A: Divide the total by (1 + percentage as decimal).

• Total with 10% tax is .
• 110 / 1.10 = original price.

Conclusion

Mastering percentages saves you money. Whether checking a receipt, calculating a tip, or negotiating a salary raise, these simple formulas are essential life skills.