How to Calculate Percentage - Complete Guide with Examples 2025
Master Percentage Calculations
To calculate a percentage, use the formula: Percentage = (Part ÷ Whole) × 100. For example, to find what percent 25 is of 200, divide 25 by 200 and multiply by 100, giving you 12.5%. To find a percentage of a number (like 15% of 80), multiply the number by the percentage divided by 100: 80 × 0.15 = 12. For percentage increase or decrease, use: ((New Value - Original Value) ÷ Original Value) × 100. These three formulas cover most percentage calculations you will encounter in shopping discounts, grade calculations, financial analysis, and everyday math.
What is a Percentage?
A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin "per centum," meaning "by the hundred." When you see 25%, it means 25 out of every 100, or simply 25/100 = 0.25.
Key Concept:
Percentage (%) = (Part / Whole) × 100
The Three Basic Percentage Calculations
Most percentage problems fall into three categories. Understanding these will help you solve almost any percentage question you encounter.
1. Finding What Percent One Number is of Another
Formula: Percentage = (Part ÷ Whole) × 100
Example: What percentage is 25 of 200?
Percentage = (25 ÷ 200) × 100 = 12.5%
So, 25 is 12.5% of 200.
2. Finding a Percentage of a Number
Formula: Result = (Percentage ÷ 100) × Number
Example: What is 15% of 80?
Result = (15 ÷ 100) × 80 = 0.15 × 80 = 12
So, 15% of 80 is 12.
3. Finding the Original Number from a Percentage
Formula: Original = Result ÷ (Percentage ÷ 100)
Example: 20 is 25% of what number?
Original = 20 ÷ (25 ÷ 100) = 20 ÷ 0.25 = 80
So, 20 is 25% of 80.
Try Our Free Percentage Calculator!
Skip the math - get instant, accurate percentage calculations with visual charts
Calculate Percentages Now →Percentage Increase and Decrease
Understanding percentage change is crucial for comparing values, analyzing trends, and making informed decisions in business and personal finance.
Percentage Increase Formula
Use this when a value has grown from an original to a new, larger value.
Formula:
% Increase = ((New Value - Original Value) ÷ Original Value) × 100
Example: Stock price increased from $50 to $65
% Increase = ((65 - 50) ÷ 50) × 100 = (15 ÷ 50) × 100 = 30%
The stock increased by 30%.
Percentage Decrease Formula
Use this when a value has decreased from an original to a new, smaller value.
Formula:
% Decrease = ((Original Value - New Value) ÷ Original Value) × 100
Example: Product price dropped from $120 to $90
% Decrease = ((120 - 90) ÷ 120) × 100 = (30 ÷ 120) × 100 = 25%
The price decreased by 25%.
Converting Between Percentages, Decimals, and Fractions
Being able to convert between these forms makes percentage calculations much easier.
% to Decimal
Divide by 100
25% = 0.25
Decimal to %
Multiply by 100
0.75 = 75%
Fraction to %
Divide, then × 100
3/4 = 75%
Real-World Percentage Examples
Shopping Discounts
A $80 shirt is on sale for 30% off. What's the sale price?
Discount = 30% of $80 = 0.30 × 80 = $24
Sale Price = $80 - $24 = $56
Calculating Tips
Your restaurant bill is $65. What's a 20% tip?
Tip = 20% of $65 = 0.20 × 65 = $13
Total with tip = $65 + $13 = $78
Grade Calculations
You scored 45 out of 60 on a test. What percentage did you get?
Percentage = (45 ÷ 60) × 100 = 75%
Investment Returns
Your investment grew from $5,000 to $6,500. What's the return percentage?
% Return = ((6,500 - 5,000) ÷ 5,000) × 100 = 30%
Common Percentage Mistakes to Avoid
Mistake #1: Using Wrong Base Number
Always use the original/starting value as the base for percentage change calculations
Mistake #2: Confusing Percentage Points with Percentages
Going from 10% to 15% is a 5 percentage point increase, but a 50% relative increase
Mistake #3: Reversing Percentage Increase/Decrease
A 50% increase followed by a 50% decrease does NOT return you to the original value!
Important Note:
If something increases by 50% and then decreases by 50%, you end up with 75% of the original value.
Example: 100 → +50% → 150 → -50% → 75
Quick Percentage Mental Math Tricks
- 10% of any number: Move decimal one place left (250 → 25)
- 5% of any number: Find 10% and divide by 2
- 15% tip: Find 10%, then add half of that
- 20% of any number: Find 10% and double it
- 25% of any number: Divide by 4
- 50% of any number: Divide by 2
Conclusion
Understanding how to calculate percentages is a valuable life skill that you'll use in shopping, finance, work, and everyday decisions. While these formulas are straightforward, a reliable percentage calculator ensures accuracy and saves time, especially for complex calculations involving percentage change, discounts, tips, and more.
Ready to Calculate Percentages Instantly?
Use our free percentage calculator with visual pie charts. Calculate basic percentages, percentage change, tips, discounts, and markup/margin - all in one tool!
Try Percentage Calculator Free →