Percentage Calculator: Quick Math Made Easy
Master percentages with this complete guide. Learn how to calculate percentage increase, decrease, tips, grades, and more — with formulas and real-world examples.
What Is a Percentage?
A percentage is a way of expressing a number as a fraction of 100. The word "percent" literally means "per hundred" (from the Latin per centum). When we say 25%, we mean 25 out of every 100, or 25/100, or 0.25 as a decimal.
Percentages are everywhere in daily life: sales discounts, tax rates, grades, interest rates, survey results, and nutrition labels. Understanding how to calculate them quickly is one of the most practical math skills you can have.
Common Percentage Calculations
| Calculation | Formula | Example |
|---|---|---|
| X% of a number | Number x (X / 100) | 20% of 150 = 150 x 0.20 = 30 |
| What % is A of B? | (A / B) x 100 | 45 out of 60 = (45/60) x 100 = 75% |
| Percentage increase | ((New - Old) / Old) x 100 | $80 to $100 = ((100-80)/80) x 100 = 25% |
| Percentage decrease | ((Old - New) / Old) x 100 | $100 to $75 = ((100-75)/100) x 100 = 25% |
| Percentage change | ((New - Old) / Old) x 100 | Positive = increase, Negative = decrease |
Essential Formulas
Finding a Percentage of a Number
The simplest calculation: multiply the number by the percentage as a decimal.
Result = Number x (Percentage / 100)
Example: 15% of 240 = 240 x 0.15 = 36
Finding What Percentage One Number Is of Another
Divide the part by the whole and multiply by 100.
Percentage = (Part / Whole) x 100
Example: 18 out of 24 = (18/24) x 100 = 75%
Percentage Increase/Decrease
Find the difference, divide by the original, multiply by 100.
% Change = ((New - Old) / Old) x 100
Example: Salary raised from $50,000 to $55,000 = ((55000-50000)/50000) x 100 = 10%
Real-World Applications
- Shopping discounts: A $80 jacket at 30% off saves you $24 (80 x 0.30). You pay $56.
- Tips at restaurants: A 20% tip on a $45 bill is $9 (45 x 0.20).
- Grade calculations: If you scored 42 out of 50, your percentage is 84% (42/50 x 100).
- Tax calculations: A 8.5% sales tax on a $200 purchase adds $17 (200 x 0.085).
- Interest rates: A $1000 savings account at 5% annual interest earns $50 per year.
Try it now: Open the Percentage Calculator →
Calculate any percentage instantly. Handles increase, decrease, and "what percent of" problems.
Frequently Asked Questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. Example: 25% of 200 = (25 x 200) / 100 = 50. Or use the decimal method: 0.25 x 200 = 50.
How do I calculate percentage increase?
Formula: ((New Value - Old Value) / Old Value) x 100. Example: Price went from $80 to $100. ((100-80)/80) x 100 = 25% increase.
What percentage do I need on the final to get an A?
Use this formula: (Desired Grade - Current Grade x Weight of Current Work) / Weight of Final. Example: You have 85% (worth 70% of grade) and need 90% overall. (90 - 85x0.7) / 0.3 = 101.7% — not possible, so aim for the highest possible grade.