Percentage Calculator
Three quick percentage tools in one. Fill in any of the calculators below and the answer appears instantly.
Reviewed by the ToolNestr Editorial Team — July 2026
What is X% of a number?
X is what percent of Y?
Percentage increase / decrease
How percentage calculations work
Three fundamental formulas power every percentage scenario you encounter. Understanding these lets you verify any percentage calculation mentally and catch errors before they cost you money.
Mode 1: X% of Y
Formula: Result = Y × X ÷ 100. Example: 20% of 150 = 150 × 20 ÷ 100 = 30. Used for tips, tax, discounts, and commissions.
Mode 2: X is what % of Y
Formula: Result = X ÷ Y × 100. Example: 30 is what % of 150? 30 ÷ 150 × 100 = 20%. Used for scores, proportions, and comparisons.
Mode 3: % change
Formula: Result = (New - Old) ÷ |Old| × 100. Example: 80 to 100 = (100-80) ÷ 80 × 100 = +25%. Used for growth, inflation, and performance.
Worked example: Asymmetric percentage changes
A $100 item gets a 50% markup: new price = $150. Then it goes on sale at 50% off: $150 × 0.50 = $75. A 50% increase followed by a 50% decrease does NOT return to the original price — this asymmetry is why percentage changes must always be applied carefully.
Why percentages matter in daily life
Percentages are the most common mathematical concept you use outside the classroom. From calculating a restaurant tip to understanding interest rates, from exam scores to investment returns — knowing how to work with percentages saves you money and helps you make informed decisions. This calculator handles the three most common questions so you never need pen and paper.
Shoppers
Calculate sale discounts, compare "X% off" vs "Y% more free" offers, and understand true savings. Mode 1 is your go-to.
Finance & Business
Model growth rates, profit margins, tax calculations and interest. Mode 3 is essential for tracking period-over-period changes.
Students
Calculate exam scores as percentages, work out grade improvements, and check assignment weightings — all essential for academic tracking.
Data Analysts
Quickly compute proportions, growth rates and relative changes in datasets. Great for sanity-checking numbers before reporting.
How to use the percentage calculator
Pick your mode
Choose the calculator that matches your question — percent of, percent of another, or change.
Enter your numbers
Type the values into the input fields. The answer updates instantly as you type.
Read the result
The answer appears in bold. Use the other modes for different types of percentage questions.
Common percentage mistakes to avoid
Wrong base for percentage change
Always divide by the original (old) value, not the new value. An increase from 50 to 100 is +100%, not +50%.
Confusing percentage points with percent
If an interest rate rises from 5% to 7%, that is a 2 percentage point increase but a 40% increase in the rate. These are not the same.
Adding percentages directly
A 20% discount followed by an extra 10% off is NOT 30% off. The second discount applies to the already-reduced price. Total saving: 28%, not 30%.
When to use the percentage calculator
The percentage calculator handles three of the most common percentage scenarios encountered in daily life. Use Mode 1 (X% of a number) whenever you need to calculate a portion of a total. Shoppers use it to determine sale discounts: 30% off a $120 jacket equals $36 in savings, bringing the final price to $84. Restaurant diners calculate tips by finding 15% or 20% of their pre-tax bill. Homebuyers estimate their down payment by calculating a percentage of the property price.
Mode 2 (X is what percent of Y) is ideal for proportions and comparisons. Students use it to convert test scores into percentages: a score of 42 out of 60 equals 70%. Business analysts calculate market share by dividing a company's revenue by the total market revenue. Fitness enthusiasts track body fat percentage or macronutrient ratios. Investors calculate the percentage of their portfolio allocated to different asset classes.
Mode 3 (percentage increase or decrease) is essential for tracking change over time. Financial analysts measure quarterly revenue growth: revenue rising from $500,000 to $625,000 represents a 25% increase. Homeowners track property value appreciation. Employers calculate salary increase percentages for annual reviews. Economists measure inflation rates by comparing price indices across periods.
The calculator is also useful for verifying manual calculations. When reviewing a bill with a service charge, a tax addition, or a volume discount, quickly entering the numbers into the appropriate mode confirms whether the applied percentage is correct and helps catch billing errors before payment.
Limitations and considerations
The percentage calculator is designed for straightforward percentage operations, but there are scenarios where additional nuance is required. The asymmetric nature of percentage change is one of the most commonly misunderstood concepts. A 50% increase followed by a 50% decrease does not return to the original value. This becomes critical in financial contexts: if an investment drops by 20%, it needs a 25% gain just to break even, not 20%. Understanding this asymmetry prevents costly misinterpretation of percentage changes.
Second, the calculator does not handle compound percentages. If you need to apply multiple sequential percentages such as a 10% discount followed by an additional 5% loyalty discount, the total discount is not 15% but 14.5%. Each percentage applies to a progressively smaller base. Similarly, compound interest calculations require iterative or exponential formulas that go beyond simple percentage operations.
Third, percentage points and percent are different concepts. A rise in interest rates from 5% to 7% is a 2 percentage point increase but a 40% increase in the rate itself. Using the wrong terminology can lead to miscommunication in financial discussions, policy debates, and data reporting.
Fourth, Mode 3 requires a non-zero old value. If the old value is zero, the percentage change is mathematically undefined due to division by zero. Additionally, very small old values can produce extremely large percentage changes that may be misleading. Always consider the absolute magnitude alongside the percentage change for a complete picture.
Frequently asked questions
How do I find a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 20% of 150 is 150 x 20 / 100 = 30. The first calculator does this for you.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, then multiply by 100. The third calculator handles increases and decreases automatically.
What is the difference between the three calculators?
The first finds a percentage of a number, the second finds what percent one number is of another, and the third finds the percentage change between two numbers.
Why isnt a 20% increase then a 20% decrease back to the start?
Each percentage applies to a different base. +20% of 100 is 120, but -20% of 120 is 96 — not 100. So equal percentage moves up and down do not cancel out.
How do I find the original price before a percentage was added?
Divide the final amount by (1 + percentage/100). For example, if a price is 120 after a 20% increase, the original was 120 / 1.20 = 100.
Is it private?
Yes — all calculations happen in your browser.
Can percentages be negative?
A negative percentage typically indicates a decrease. Mode 3 shows increases with a + sign and decreases with a - sign, making it easy to see the direction of change.
How do I calculate a percentage difference between two numbers?
Use Mode 3. Enter the old value first, then the new value. The calculator shows the percentage change, with a + sign for increases and - for decreases.