How to Calculate Percentage: Formulas and Examples

Percentages show up everywhere, from a discount tag to a test score to a salary raise, yet many people freeze when they have to work one out on the spot. The truth is that every percentage question reduces to one of a handful of simple formulas. Master those and the math becomes second nature.

What a Percentage Really Is

A percentage is just a fraction out of 100. The word literally means per hundred. When you say 25 percent, you are saying 25 out of every 100, or the fraction 25 over 100, which equals 0.25 as a decimal. Switching between these three forms, fraction, decimal and percent, is the foundation of every calculation that follows.

To turn a percentage into a decimal, divide by 100. To turn a decimal back into a percentage, multiply by 100. That one move unlocks almost everything.

Finding a Percentage of a Number

This is the most common question: what is X percent of Y. The formula is to convert the percentage to a decimal and multiply by the number.

For example, to find 20 percent of 150, change 20 percent to 0.20, then multiply by 150. The answer is 30. Whether you are calculating a tip, a discount or a tax, the method never changes. A shirt marked 30 percent off a price of 80 saves you 0.30 times 80, which is 24, leaving a final price of 56.

What Percent One Number Is of Another

Sometimes you have two numbers and want to know their relationship as a percentage. The formula is the part divided by the whole, multiplied by 100.

Suppose you answered 45 questions correctly out of 60. Divide 45 by 60 to get 0.75, then multiply by 100 for a score of 75 percent. The same approach tells you what share of a budget a single expense represents, or how much of a goal you have reached.

Percentage Increase and Decrease

Tracking change over time calls for the percentage change formula. Subtract the old value from the new value, divide by the old value, then multiply by 100.

If a subscription price climbs from 80 to 100, the increase is (100 minus 80) divided by 80, times 100, which is 25 percent. The same formula handles decreases, you simply get a negative result. A price falling from 100 to 75 is a change of (75 minus 100) divided by 100, times 100, or negative 25 percent, meaning a 25 percent drop. Always divide by the original value, not the new one, or the answer will be wrong.

A Quick Worked Example

Imagine your monthly grocery bill rose from 400 to 470 and you want to know the increase and the new total relative to your 2,000 budget.

For the increase, take (470 minus 400) divided by 400, times 100, which is 17.5 percent. To see what share groceries now take of your budget, divide 470 by 2,000 and multiply by 100, giving 23.5 percent. In two quick calculations you understand both how fast the cost is rising and how much of your money it consumes.

How to Use the Percentage Calculator

When you would rather not reach for the formulas, the Percentage Calculator handles all of these cases in one place. Typical steps are:

1. Pick the type of calculation, such as percent of a number, percentage increase or what percent of.
2. Enter your two values in the labeled fields.
3. Read the answer instantly, with the working shown so you understand it.

Because the Percentage Calculator updates as you type, it is easy to check homework, verify a discount at the register or confirm a raise offer in seconds. There is no signup and nothing to install.

Everyday Uses Worth Knowing

A solid grasp of percentages pays off constantly:

• Shopping: confirm that a sale price matches the advertised discount.
• Tips and tax: add the right amount to a bill without guesswork.
• Finance: compare interest rates, returns and fees on an equal footing.
• Work and study: track progress toward targets and grade results.

For money-specific calculations like interest growth or loan costs, the related calculators build on these same percentage basics.

Conclusion

Every percentage problem you are likely to meet fits one of three formulas: a percentage of a number, what percent one value is of another, or percentage change between two values. With those in hand you can solve almost anything by mental math or a quick check. Run your numbers through the Percentage Calculator when you want speed and certainty, and explore the rest of the free all tools for more everyday math.