Calculate Percentage Increase, Decrease, and Share Instantly
Shopping discounts, salary raises, tax rates, and survey results all come down to percentages. The most common mistakes are not arithmetic errors but wrong formulas: adding 10 percent to 200 is not the same as finding what percent 20 is of 200. Each situation needs a different operation, and mixing them up changes the answer.
This percentage calculator bundles the three operations people actually need: percentage of a number, percentage increase, and percentage decrease. It also answers the reverse question, what percent one value is of another. Every result updates as you type, with the step shown so you can follow the math and catch mistakes before they matter.
How to Use the Percentage Calculator
- Choose the operation you need, such as increase, decrease, or what percent of.
- Enter the base value, for example the original price of an item.
- Enter the percentage, such as
15for a 15 percent change. - Read the result, which updates live as you adjust either input.
- Review the calculation step to confirm the formula matches your intent.
- Reset and repeat for follow-up values like stacked discounts.
Example Calculations
A store applies a 20 percent discount to a $50 jacket, and a shopper wants to know what percent $15 is of $60.
| Operation | Input | Result |
|---|---|---|
| Percentage of | 15% of 200 | 30 |
| Increase | 50 + 20% | 60 |
| Decrease | 50 - 20% | 40 |
| What percent of | 15 of 60 | 25% |
Understanding the Formulas
Percentage of a number multiplies the base by the rate, so 15 percent of 200 is 200 * 0.15 = 30. An increase multiplies by 1 + rate; a decrease multiplies by 1 - rate. The reverse question divides the part by the whole, so 15 divided by 60 is 0.25, or 25 percent. Keeping these four patterns in mind makes most everyday math predictable.
Tips for Correct Percentage Math
- Pick the right operation — a discount is a decrease, a price hike is an increase, and a test score is a what-percent-of question.
- Do not add percentages blindly — a 10 percent discount followed by another 10 percent is not 20 percent off the original price.
- Convert rates carefully — divide the percentage by 100 before multiplying, since 25 percent is 0.25 as a rate.
- Mind the base value — a percentage increase changes the base for any later percentage, which is how compound interest grows.
- Round only at the end — keep full precision during the calculation and round the final amount for money.
When to Use This Tool
- Comparing discounts — decide whether 30 percent off or a flat amount saves more on a purchase.
- Budgeting changes — apply a rent increase or utility rise to a monthly budget quickly.
- Grading and scoring — turn raw scores into percentages for tests, quizzes, and progress tracking.
- Business margins — compute markup percentages and sale reductions without spreadsheet formulas.
- Data reporting — express survey counts and usage metrics as shares of a total.
Frequently Asked Questions
How do I calculate 15 percent of a number?
Multiply the number by 15 and divide by 100, or simply multiply by 0.15; for 200, the result is 30.
What is the difference between increase and decrease?
An increase adds a percentage of the base value to it, while a decrease subtracts that percentage from it.
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100, so 15 of 60 is 15 / 60 * 100, which equals 25 percent.
How do I add 10 percent to a price?
Multiply the price by 1.10, so a 50 unit price becomes 55 after a 10 percent increase.
Why are stacked discounts not additive?
Each discount applies to the already-reduced price, so two 10 percent cuts reduce the original by only 19 percent.
Can I calculate a percentage decrease below zero?
Decreasing by more than 100 percent yields a negative result, which is unusual in real purchases and flagged by the tool.
How is a percentage of a number different from a ratio?
A percentage is a ratio scaled to 100, so 0.25 as a ratio is the same quantity as 25 percent.
Does the calculator work with decimals?
Yes, base values and percentages can include decimals, such as 12.5 percent of 48.60, and results keep their precision.