Percentages appear everywhere — discounts, tips, tax, grades, statistics. This guide explains the three main types of percentage calculations and how to solve them instantly.
⚡ Try It Free — No Signup
Works instantly in your browser. No account, no install.
Open Percentage Calculator →The Three Types of Percentage Problems
1. What is X% of Y?
Formula: Result = (X / 100) × Y
Example: What is 20% of 250? → (20/100) × 250 = 50
2. X is what percent of Y?
Formula: Percent = (X / Y) × 100
Example: 45 is what percent of 180? → (45/180) × 100 = 25%
3. Percentage Change
Formula: Change% = ((New - Old) / Old) × 100
Example: Price changed from $80 to $100 → ((100-80)/80) × 100 = +25%
Common Percentage Uses
| Scenario | Formula |
|---|---|
| Sale discount | Price × (1 - Discount%/100) |
| Tax | Price × (1 + Tax%/100) |
| Tip | Bill × Tip%/100 |
| Grade | (Points earned / Total points) × 100 |
| Interest rate | Principal × Rate%/100 |
Frequently Asked Questions
How do I calculate 15% tip?
Multiply the bill by 0.15. For a $60 bill: 60 × 0.15 = $9 tip. Or use the calculator — enter 15% of 60.
What's the difference between percentage and percentage points?
If interest rates rise from 2% to 3%, that's a 1 percentage point increase, but a 50% increase in the rate. These are different things.
How do I reverse a percentage (find the original value)?
If the final value is $120 after a 20% increase: Original = 120 / 1.20 = $100.
How do I calculate percentage decrease?
Same as percentage change: ((New - Old) / Old) × 100. A negative result means a decrease.