What is a Percentage Calculator?
A percentage calculator is a simple tool that automates common math you encounter at school, work, and in daily life. Whether you’re figuring out discounts while shopping, calculating tips at a restaurant, analyzing growth rates in finance, or comparing test scores, percentages turn raw numbers into easy-to-understand proportions. This calculator streamlines four core tasks: percentage of a number, what percent a number is of another, increasing or decreasing a number by a percentage, and percentage change between two values.
How to Use the Percentage Calculator
- Choose a calculation type from the dropdown list.
- Fill in only the fields referenced for that calculation (leave others blank).
- Click Calculate to instantly see a precise result.
Supported calculations
- Find A% of B: Enter a Percent and a Number. Example: 15% of 200.
- What percent is A of B: Enter Part and Whole to learn the percentage one number represents of another.
- Increase a number by A%: Enter Original value and Change percent to apply a markup, tax, or growth rate.
- Decrease a number by A%: Enter Original value and Change percent to apply a discount or depreciation.
- Percent change from old to new: Enter Old value and New value to measure growth or decline.
Formulas Used
1. Percentage of a number
Result = (Percent / 100) × Number
Example: 15% of 200 = 0.15 × 200 = 30.
2. What percent is A of B
Percent = (Part / Whole) × 100
Example: 30 is what percent of 120? 30 / 120 × 100 = 25%.
3. Increase by percentage
New value = Original × (1 + Percent/100)
Example: Increase 80 by 12.5%: 80 × 1.125 = 90.
4. Decrease by percentage
New value = Original × (1 - Percent/100)
Example: Decrease 80 by 12.5%: 80 × 0.875 = 70.
5. Percent change
Percent change = [(New - Old) / Old] × 100
Example: From 50 to 65: (15 / 50) × 100 = 30% increase.
Common Use Cases
- Shopping: Quickly calculate discounts (decrease by percent) or sales tax (increase by percent).
- Finance: Measure investment returns (percent change) or allocate budgets by percentage.
- Education: Check what percent a score is of the total or convert grades.
- Health & Fitness: Track percentage changes in weight, repetitions, or time goals.
- Business Analytics: Compare month-over-month KPIs and compute growth or decline.
Tips for Accurate Results
- Use the correct fields for the chosen calculation and leave unrelated fields blank.
- Double-check the Whole value isn’t zero when finding what percent A is of B.
- For money, consider rounding results to two decimal places for readability.
- Remember that percent change can be positive (increase) or negative (decrease).
Why This Percentage Calculator?
It’s fast, flexible, and covers the most common scenarios so you don’t need separate tools. You can switch calculations instantly, reuse entered values across scenarios, and rely on consistent formulas that match textbooks and professional practice. Whether you’re a student checking homework or a manager reviewing metrics, this calculator keeps your percentage math clear and error-free.
