Percentage Calculator

How to Use the Percentage Calculator

Our percentage calculator offers three powerful modes to handle all your percentage calculation needs. Simply choose the mode that matches your question, enter the values, and click "Calculate" to get an instant result.

Mode 1 — "X% of Y": Use this when you need to find a percentage of a number. For example, "What is 15% of 300?" Enter 15 and 300 to get 45. This mode is commonly used for calculating tips, discounts, taxes, and commissions.

Mode 2 — "X is what % of Y": Use this when you know two numbers and want to find what percentage one is of the other. For example, "75 is what percent of 250?" Enter 75 and 250 to get 30%. This is ideal for calculating test scores, completion rates, and proportional comparisons.

Mode 3 — "% Change": Use this to calculate the percentage increase or decrease between two values. For example, "From 200 to 250" gives a 25% increase. This mode is widely used in financial analysis, sales comparison, and performance evaluation.

Understanding Percentages

A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin "per centum," meaning "by the hundred." Percentages are used universally in everyday life, from shopping discounts to exam scores, from interest rates to battery levels.

The mathematical formula for calculating a basic percentage is simple: To find X% of Y, multiply Y by X and divide by 100. To find what percentage X is of Y, divide X by Y and multiply by 100. For percentage change, subtract the old value from the new value, divide by the old value, and multiply by 100.

Real-World Applications of Percentages

Shopping and Discounts

When a store advertises a 30% off sale, you can quickly calculate the discount amount using Mode 1. If an item costs $85 and is 30% off, the discount is $25.50, making the final price $59.50. Understanding percentages helps you evaluate whether a sale offers genuine value.

Finance and Investing

Interest rates, investment returns, and loan calculations all rely heavily on percentages. A savings account with a 4.5% annual interest rate on a $10,000 balance earns $450 per year. Understanding percentage change is crucial for evaluating stock performance, comparing investment options, and tracking portfolio growth.

Grades and Test Scores

Academic grading almost universally uses percentages. If you scored 42 out of 50 on a test, Mode 2 tells you that is 84%. Knowing how to calculate your grade percentage helps you track your academic performance and set improvement goals.

Health and Nutrition

Nutritional labels express daily values as percentages. If a food item contains 15% of your daily calcium needs, understanding percentages helps you plan a balanced diet. Body fat percentage, hydration levels, and many health metrics are also expressed as percentages.

Common Percentage Formulas

• X% of Y = Y × (X / 100)
• X is what % of Y = (X / Y) × 100
• % Increase = ((New - Old) / Old) × 100
• % Decrease = ((Old - New) / Old) × 100

Tips for Working with Percentages

• To quickly estimate 10% of any number, simply move the decimal point one place to the left.
• To find 5%, calculate 10% first and then halve it.
• Percentage increase and decrease are not symmetric: a 50% increase followed by a 50% decrease does not return to the original value.
• When comparing percentage changes, always pay attention to the base value — a 10% increase on $1,000 is very different from a 10% increase on $100.