What Is a Percentage?

A percentage is a way of expressing a number as a fraction of 100. The word itself comes from the Latin per centum, meaning "by the hundred." When you say something is 25%, you mean 25 out of every 100 parts — the same amount as the fraction 25/100 or the decimal 0.25. Percentages give people a common, easy-to-compare scale for describing proportions, whether you're looking at a discount at checkout, a grade on a test, an interest rate on a loan, or the year-over-year growth of a business. Because everyone reads percentages the same way, they've become the default language for comparing parts to wholes across finance, science, retail, and everyday conversation.

How This Percentage Calculator Works

This tool covers the four situations people run into most often when they need to work with percentages:

• % of a number — Find a percentage of any value, such as calculating a 15% tip on a $200 bill.
• What % is X of Y — Work out what percentage one number represents of another, such as figuring out what share of a $200 budget a $30 expense takes up.
• Find the whole — Given a part and its percentage, calculate the original total, useful when you know a discount amount and the discount rate but need the full price.
• % increase / decrease — Measure how much a value has grown or shrunk between two points, handy for tracking price changes, weight loss goals, or sales growth.

Enter your numbers into any tab and press Calculate (or just tab out of the field) to see an instant result on the display panel. All four calculators accept decimals and negative numbers, and results update without reloading the page.

Percentage Formulas You Can Use By Hand

If you'd rather work it out yourself, here are the formulas behind each calculator:

• Percent of a number: (Percent ÷ 100) × Number
• What percent X is of Y: (X ÷ Y) × 100
• Finding the whole: X ÷ (Percent ÷ 100)
• Percentage change: ((New − Old) ÷ Old) × 100

A positive result in the percentage-change formula means an increase; a negative result means a decrease. These four formulas are all variations of the same underlying relationship between a part, a whole, and a rate — once you know one formula, the others follow the same logic in reverse.

Everyday Uses for Percentage Calculations

Percentages show up far more often than most people realize. Shoppers use them to work out discounts and sales tax at checkout. Diners use them to calculate tips at restaurants. Students and teachers use them to convert raw test scores into grades. Investors use them to track returns, interest rates, and portfolio allocation. Businesses use them to report growth, profit margins, and market share. Nutrition labels use them to show the percentage of a daily recommended value in a serving of food. Even fitness tracking, such as calculating body fat percentage or a change in body weight over time, relies on the same basic percentage math this calculator handles.

Percentage Formula

Every calculator on this page comes from one core formula: Percentage = (Part ÷ Whole) × 100. Rearranging that same formula gives you the other three calculators above — solve for the part, the whole, or the percentage depending on which two values you already know.

Percentage Calculator: Difference vs. Change

"Percentage change" (used in the % increase/decrease tab above) measures how far a value has moved from its starting point, so it treats the first number as the baseline: ((New − Old) ÷ Old) × 100. "Percentage difference" is different — it compares two values without treating either as a baseline, which is useful when you're comparing two independent measurements rather than a before-and-after. Its formula is: |Value 1 − Value 2| ÷ ((Value 1 + Value 2) ÷ 2) × 100. Use percentage change for growth, discounts, and price history; use percentage difference for comparing two products, test groups, or readings side by side.

Percentage Calculator of Marks (Grades and Exam Scores)

To turn a test score into a percentage, divide the marks obtained by the total possible marks, then multiply by 100: (Marks Obtained ÷ Total Marks) × 100. For example, scoring 78 out of 90 works out to (78 ÷ 90) × 100 = 86.67%. You can run this directly in the "What % is X of Y" tab above — enter 78 as X and 90 as Y.

Percentage Calculator in Excel

Excel uses the same math, just written as a cell formula. To find what percentage one cell is of another, use =A1/B1 and format the cell as Percentage — Excel applies the ×100 automatically once the cell's number format is set. To find a percentage of a number, use =A1*15% (or =A1*0.15). To calculate percentage change between two cells, use =(B1-A1)/A1 and format the result as a percentage.

Number to Percentage Calculator

To convert a decimal or fraction into a percentage, multiply it by 100 and add the % sign — a decimal like 0.42 becomes 42%, and a fraction like 3/8 (0.375) becomes 37.5%. Going the other direction, divide a percentage by 100 to get back to a decimal: 60% becomes 0.6.

Percentage Calculator for Money: Discounts, Tips, and Sales Tax

Money math is one of the most common uses of percentages. To find a discount, calculate the percentage off using the "% of a number" tab, then subtract that from the original price — a 20% discount on a $50 item saves $10, bringing the price to $40. Tips work the same way: an 18% tip on a $65 bill is $11.70. For sales tax, add the calculated percentage to the original amount instead of subtracting it.

Profit Percentage Calculator

Profit percentage measures how much profit you made relative to what something cost, not relative to the selling price: ((Selling Price − Cost Price) ÷ Cost Price) × 100. For example, if you buy an item for $40 and sell it for $52, your profit is $12, and your profit percentage is (12 ÷ 40) × 100 = 30%. You can calculate this using the "What % is X of Y" tab — enter your profit amount ($12) as X and your cost price ($40) as Y.

Tips for Getting Accurate Results

A few habits help avoid common percentage mistakes. Always double-check which number is the "whole" and which is the "part" before plugging values in — mixing them up is the most frequent source of error. When comparing a change over time, remember that percentage increase and percentage decrease are not symmetric: a 50% increase followed by a 50% decrease does not bring you back to the starting value. Finally, keep an eye on rounding — for financial calculations, it's usually best to carry a couple of extra decimal places until the very last step.

Frequently Asked Questions