Percentage Calculator
Calculate percentages, percent change, increase, decrease, and difference with step-by-step formulas
Check Percentage Calculator
Formula result
Copy-ready result handoff
Use this after calculating a percent of a number, percent change, or percentage difference.
Confirm the base value that represents 100%.
Percent change uses the old value as the denominator; percentage difference compares values against their average.
Copy this after replacing the bracketed result with the value shown by the calculator.
Percentage result: [paste the displayed percent, part, or change result]. Inputs checked: Confirm the base value that represents 100%. Assumption: Percent change uses the old value as the denominator; percentage difference compares values against their average. Use case: Discount, grade, markup, tax, tip, and percent change checks. Next check: Use Percent Error when one value is a measured result and the other is an accepted reference.
Choose the percentage form first: part of a whole, percent of a value, percent change, percentage difference, or reverse percentage. The formula guide below keeps the base value visible so each result is easier to check.
How the result is built
Formula, Variables, And Worked Example
The percent is the rate, the base is the 100% reference value, and the result is the part being calculated.
To find 18% of 250, calculate 18 / 100 * 250 = 45. The base stays 250, and 45 is the part represented by 18%.
- Using the new value as the base when the old value is 100%.
- Adding percentage changes that were calculated from different bases.
- Confusing percentage points with percent change.
- The base value is the quantity that represents 100%.
- Percentage change uses the old value as the denominator.
- Percentage difference compares two values against their average.
Percentage Formulas, Examples, And Mistakes
Choosing the right percentage calculation
Use percent of a number when the question asks for a part of a known whole. Use percent change when there is a before value and an after value. Use percentage difference when you are comparing two values without treating either one as the original baseline.
Base value and percentage points
The base is the value that represents 100%. Changing the base changes the meaning of the percentage, which is why successive discounts or increases cannot simply be added. Percentage points describe the direct gap between two percentages, while percent change describes relative movement from a baseline.
Related tools
Use the Fraction Calculator for exact part-whole arithmetic, the Ratio Calculator for proportions, and the Percent Error Calculator when one value is a measured result and the other is an accepted reference.
Common result checks
Questions about this tool
- How do I calculate a percentage of a number?
- Convert the percent to a decimal by dividing by 100, then multiply by the base number. For example, 18% of 250 is 0.18 * 250 = 45.
- What is the formula for percent increase or decrease?
- Percent change is (new value - old value) / old value * 100. A positive result is an increase, and a negative result is a decrease.
- When should I use percentage difference instead of percent change?
- Use percent change when one value is the original baseline. Use percentage difference when you are comparing two values without treating either one as the starting value.
- Can I use this calculator for discounts, grades, and tips?
- Yes. The same percent-of-a-number and percent-change modes work for retail discounts, grade percentages, sales tax, tips, markups, and quick business checks.