Percentage Calculator
Select calculation type and enter values to get instant results
X% of Y
Calculate percentage of a number
X is what % of Y
Find what percentage X is of Y
% Change
Calculate percentage increase/decrease
Calculation Results
Result of your percentage calculation
Understanding the Formula
Percentage calculation formula explained in detail.
Common Percentage Calculations
Quick reference for everyday percentage calculations
Shopping & Discounts
- 20% discount: Multiply price by 0.8
- 15% tip: Multiply bill by 0.15
- Sales tax (8%): Multiply by 1.08
- Price after discount: Original × (1 - %/100)
Finance & Growth
- Interest rate: (Interest/Principal) × 100
- Profit margin: (Profit/Revenue) × 100
- Growth rate: [(New - Old)/Old] × 100
- Annual return: (End Value/Start Value - 1) × 100
Quick Tips
For quick mental calculations: 10% of any number is moving the decimal one place left. 5% is half of 10%. 1% is moving the decimal two places left. Combine these for other percentages!
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Understanding Percentage Basics
The foundation of all percentage calculations
What is a Percentage?
A percentage is a way of expressing a number as a fraction of 100. It is often denoted using the percent sign, "%". For example, 45% means 45 out of 100, or 45/100.
Three Core Types
Most percentage problems fall into three categories: finding the part (X% of Y), finding the percentage (X is what % of Y), and finding the whole (X is Y% of what). Our calculator handles all three effortlessly.
Key Formulas
- Part = (Percentage/100) × Whole
- Percentage = (Part/Whole) × 100
- Whole = Part × (100/Percentage)
- Change = ((New - Old)/Old) × 100
Real‑World Applications of Percentages
Where you'll use percentages every day
Discounts & Sales
When you see "30% off", you can instantly calculate the savings and final price using the "X% of Y" mode.
Tips & Service Charges
In many countries, leaving a 10–20% tip is customary. Our calculator helps you split bills and calculate exactly how much to leave.
Financial Planning
From interest rates on loans to returns on investments, percentages are everywhere in personal finance. Use the percentage change tool to track growth.
Academic Grades
Teachers often express scores as percentages. You can quickly find out what grade you need on a final exam to achieve a desired course percentage.
Statistics & Data
Percentages are used to compare proportions in surveys, polls, and scientific data. They make large numbers easier to understand.
Percentage Tips & Tricks
Mental math shortcuts for everyday calculations
10% Trick
To find 10% of any number, just move the decimal one place to the left. For example, 10% of 250 is 25.0.
5% Trick
5% is half of 10%. So first find 10%, then divide by 2. 5% of 250 = 10% (25) ÷ 2 = 12.5.
1% Trick
Move the decimal two places left to get 1%. 1% of 250 = 2.5. Then you can multiply to get 2%, 3%, etc.
Combining Tricks
Need 15%? That's 10% + 5%. For 20% off, just subtract 10%×2. Once you know the base tricks, you can build any percentage quickly.
Quick Example
What's 15% of 80? 10% = 8, 5% = 4, so 15% = 8 + 4 = 12. No calculator needed!
Common Mistakes to Avoid
Pitfalls that can throw off your calculations
Misplacing the Decimal
Remember: 5% is 0.05, not 0.5. A misplaced decimal can make your answer 10× too large or too small.
Confusing Percentage Points vs. % Change
If a value goes from 10% to 12%, it's a 2 percentage point increase, but a 20% increase relative to the original 10%. Always clarify which one you mean.
Using the Wrong Base
For percentage change, always divide by the original (old) value, not the new one. This is a common error that leads to incorrect results.
Frequently Asked Questions
Everything you need to know about percentage calculations