Free Percentage Calculator
Percent of a number, percent change, and reverse percent problems.
- Free Forever
- No Registration Required
- Instant Results
- Downloadable Reports
- Mobile Friendly
Inputs
Result
20.00% of 150.00
30.00
Your result is ready.
Download your free detailed report — inputs, result, formula and explanation included.
Estimates only. Verify with a professional for consequential decisions.
- Always Free
- No Hidden Costs
- No Account Required
- Unlimited Calculations
- Instant Reports
Short answer
A percentage is a ratio expressed per hundred. 'X percent of Y' equals (X ÷ 100) × Y. Percent change equals (new − old) ÷ |old| × 100.
What is the Percentage Calculator?
The percentage calculator resolves the three most common percent problems: finding a percentage of a number, finding what percent one number is of another, and computing percent change between two values.
How does the Percentage Calculator work?
Divide by 100 to convert a percent to a decimal; multiply to convert back. For percent change, subtract old from new, divide by the absolute value of the old, and multiply by 100.
Formula
Variables
XPercent valueYBase amountAOriginal valueBNew value
Explanation
A percentage is a fraction with denominator 100. Multiplying by 100 converts a decimal ratio to a percent.
Examples
Example 1: 20% of 150
(20/100) × 150 = 30.
Example 2: 45 is what % of 180
45 ÷ 180 × 100 = 25%.
Example 3: % change from 80 to 100
(100 − 80) ÷ 80 × 100 = +25%.
Applications
- Sales tax and tip calculation
- Discount and markup pricing
- Grade and score conversion
- Financial return reporting
Advantages
- Instantly handles the three main percent problems
- Signed percent change distinguishes gains from losses
Limitations
- Percent change is undefined when the base value is zero
Common mistakes
- Confusing 'X% of Y' with 'X is what % of Y'
- Dividing by the new value instead of the old value in percent change
Tips
- To increase a number by P%, multiply by (1 + P/100)
- To reverse a P% increase, divide by (1 + P/100), not subtract P%
Related concepts
The Percentage Calculator sits inside the Math Calculators hub, in the algebra & equations cluster. Solving for unknowns and manipulating expressions. Understanding the terms below makes the output easier to interpret and easier to compare against neighbouring measures.
Practical use cases and industry applications
Understanding Percentage
The percentage calculator resolves the three most common percent problems: finding a percentage of a number, finding what percent one number is of another, and computing percent change between two values. Within math calculators, percentage belongs to the algebra & equations cluster, where it shares terminology and assumptions with closely related tools.
Learning how percentage is calculated
A percentage is a fraction with denominator 100. Multiplying by 100 converts a decimal ratio to a percent. Working through the variables one at a time — X, Y, A, B — makes the result reproducible by hand and easier to sanity-check.
Using percentage to make a decision
Sales tax and tip calculation Discount and markup pricing Grade and score conversion Because outputs depend on the assumptions you enter, run more than one scenario before committing to a figure.
How percentage compares with related measures
equation, root, exponent, logarithm all describe adjacent aspects of algebra & equations. Comparing this calculator's output against those measures — using the related tools listed on this page — prevents a single metric from being read in isolation.
Frequently asked questions
How do I remove a discount?
If a price after a P% discount is X, the original price is X ÷ (1 − P/100).
Is percent change symmetric?
No. Going from 100 to 120 is +20%, but going from 120 to 100 is −16.7%.
Related calculators
These tools share entities, formulas or user intent with the percentage calculator.
Financial
Free Compound Interest Calculator
Project the future value of savings with compounding and periodic contributions.
Financial
Free Loan Calculator
Compute the fixed monthly payment on any amortizing loan.
Financial
Free Tip Calculator
Split a restaurant bill with tax and tip across any number of people.
Math
Free Percentage Change Calculator
Increase or decrease between two numbers.
Math
Free Complex Number Arithmetic Calculator
Add, subtract, multiply and divide complex numbers.
Math
Free Percent Error Calculator
Absolute and percent error between a measured and accepted value.
Math
Free Cubic Equation Root Calculator
Real root(s) of ax³ + bx² + cx + d = 0.
Math
Free Exponent Calculator
Compute any base raised to any power, including fractional and negative.
Math
Free Factorial Calculator
n! for whole numbers, with digit count.