Percentage Math Made Easy (With Real Examples)
2026-05-23
Quick Answer
Quick Answer: To find X% of Y, multiply Y × (X ÷ 100). Example: 20% of $49.99 = $49.99 × 0.20 = $9.998 (about $10.00 off). Try our Percentage Calculator.
Three common percentage questions
1. What is X% of Y?
Formula: (X / 100) × Y
Shopping example: 25% off a $80 jacket → 0.25 × 80 = $20 off → pay $60.
2. X is what % of Y?
Formula: (X / Y) × 100
Test score: 42 out of 50 → (42/50) × 100 = 84%.
3. Percent change from A to B
Formula: ((B - A) / A) × 100
Price rose from $80 to $100 → ((100-80)/80) × 100 = +25%.
Percentage tips
- Convert percent to decimal by dividing by 100 (20% → 0.20).
- For mental math, 10% is easy — double it for 20%, halve it for 5%.
- Sales tax and tips are just “percent of” problems.
Try It Yourself
Use the Percentage Calculator for all three modes, or the Discount Calculator for sale prices.
Frequently Asked Questions
How do I calculate 15% tip?
Multiply the bill by 0.15, or use our Tip Calculator.
How do I find 30% off a price?
Multiply the original price by 0.30 for savings, or use the Discount Calculator.