What Does a Percentage Calculator Do?
A percentage calculator converts ratios and percentage changes into easy-to-read results. You can use it to find a percentage of a number, determine what percentage one number represents of another, calculate percentage increases or decreases, work out discount prices, and solve reverse-percentage problems.
Percentage Formulas at a Glance
$$\text{Percent of a Number} = \frac{P}{100}\times T$$
$$\text{Percent Change} = \frac{\text{New}-\text{Old}}{\text{Old}}\times100$$
Use the calculator above when the numbers are awkward, the calculation has several steps, or you simply want to check your work quickly.
How to Use Each Calculation Mode
1. Percent of a Number
To find 20% of 150, enter 20 and 150. The result is 30.
2. What Percent Is A of B?
To find what percentage 25 is of 50, enter 25 and 50. The result is 50%.
3. Percentage Increase or Decrease
Enter an old value and a new value. The calculator shows the relative percentage change and whether it increased or decreased.
4. Discount Price
Enter the original price and discount rate to see the discount amount and final price.
5. Reverse Percentage
When a known value represents a stated percentage of an original amount, this mode works backward to find the original.
Common Uses
Use percentages for marks, discounts, tax, tips, salary changes, profit margins, conversion comparisons, budgeting, and everyday business math.
Percentage vs Percentage Points
A percentage change and a percentage-point change are not the same. For example, moving from 2% to 3% is a 1 percentage-point increase. Relative to the original 2%, it is a 50% increase.
Common Percentage Mistakes
- Using the wrong whole or base value.
- Confusing “what is X% of Y?” with “X is what percent of Y?”
- Using the discounted price as the base when calculating the original discount percentage.
- Rounding too early in multi-step calculations.
- Confusing percentage points with percentage change.
Examples
| Problem | Formula | Result |
|---|---|---|
| 20% of 150 | 0.20 × 150 | 30 |
| 25 is what % of 50? | 25 ÷ 50 × 100 | 50% |
| 100 to 125 | (125−100) ÷ 100 × 100 | 25% increase |
| $200 with 15% discount | 200 − (0.15 × 200) | $170 |
Related SmartWebHub Tools
For broader financial calculations, visit the Currency Converter, EMI Calculator, Compound Interest Calculator, Investment & ROI Calculator, and Salary & Tax Calculator.
Frequently Asked Questions
How do I calculate what percent one number is of another?
Divide the part by the whole and multiply by 100.
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply it by the number.
How do I calculate percentage increase or decrease?
Subtract old from new, divide by old, and multiply by 100. The sign shows the direction.
How do I calculate a discount?
Find the discount amount with price × rate ÷ 100, then subtract that amount from the original price.
Are calculations performed in my browser?
Yes. The calculation logic runs client-side in JavaScript on this page.