Last updated: June 5, 2026

Percentage Calculator

Quickly solve any percentage-based math problem.

Percentage Calculator

Choose a percentage mode and enter the two values.

Result

Percentage calculator tools help when you need a percent answer quickly without doing mental math. This Percentage Calculator can help with percent of a number, percentage increase, percentage decrease, discounts, tips, marks, tax, price changes, and reverse percentage situations.

Percentages appear everywhere: shopping, invoices, school marks, business reports, loan rates, salary changes, analytics, recipes, and investment summaries. The math is usually simple, but mistakes are common when people rush, especially with percent change and reverse percentages.

Example percentage calculator result showing percent value, increase or decrease, and formula summary.

Table of Contents

What is a percentage calculator?

A percentage calculator is a tool that solves percent-based questions. It can find what percent one number is of another, calculate a percentage of a number, apply a percentage increase or decrease, and work backward from a final value.

The basic idea is that a percentage means a number out of 100. For example, 25 percent means 25 out of 100, or one quarter. A percentage calculator turns that idea into practical results for real numbers.

If you want to review the concept, Khan Academy has a useful percentages learning section covering percent basics, conversions, and word problems.

How to use this percentage calculator

Choose the type of percentage problem first. If you want to know 15 percent of 800, use the percent-of mode. If you want to compare old and new values, use percentage change. If you want to add or subtract a percentage from a price, use increase or decrease mode.

Enter the numbers carefully. Percent questions often fail because the wrong number is used as the base. For percentage change, the original value is the base. For discounts, the original price is the base. For marks, the total possible marks are usually the base.

After calculating, read the result and the formula summary if available. The formula helps confirm that the calculation used the correct base number.

Common percentage formulas

To find a percentage of a number, use:

Percentage value = number x percentage / 100

For example, 20 percent of 500 is 500 x 20 / 100 = 100.

To find what percent one number is of another, use:

Percent = part / whole x 100

For example, 45 out of 60 is 45 / 60 x 100 = 75 percent.

To calculate percentage change, use:

Percentage change = (new value – old value) / old value x 100

This formula is why the original value matters. Changing the base changes the result.

Percentage calculator examples

Example 1: A shirt costs $80 and has a 25 percent discount. The discount is $20, so the final price before tax is $60.

Example 2: A score is 42 out of 50. The percentage is 42 / 50 x 100 = 84 percent.

Example 3: A price increases from $200 to $250. The increase is $50. The percentage increase is 50 / 200 x 100 = 25 percent.

Example 4: A monthly expense decreases from $120 to $90. The decrease is $30. The percentage decrease is 30 / 120 x 100 = 25 percent.

Example 5: A restaurant bill is $48 and you want to leave a 15 percent tip. The tip is 48 x 15 / 100 = $7.20. The total before tax adjustments would be $55.20.

Example 6: A store shows a $1,250 laptop with a 12 percent discount. The discount is 1250 x 12 / 100 = $150, so the discounted price is $1,100 before any extra tax, fee, or shipping amount.

Example 7: A business report says sales moved from 8,000 units to 9,200 units. The increase is 1,200 units. The relative increase is 1,200 / 8,000 x 100 = 15 percent.

Reverse percentages

Reverse percentage problems start with the final value and ask for the original value. For example, if a price after a 20 percent discount is $80, the original price was not $100 because the $80 represents 80 percent of the original price.

The formula is:

Original value = final value / (percentage remaining / 100)

In the example, $80 / 0.80 = $100. Reverse percentages are common in discounts, tax-inclusive prices, price increases, and exam questions.

Reverse calculations are also useful when a final price already includes tax. If a product costs $118 including 18 percent tax, the pre-tax amount is 118 / 1.18 = $100. The tax amount is $18. This is different from subtracting 18 percent from $118, which would use the wrong base.

When you are unsure, write down what the final value represents. Is it 80 percent of the original, 118 percent of the original, or a new value after a change? That single sentence usually tells you which formula to use.

This is why reverse percent problems reward careful wording.

In school, shopping, and business reports, the base number is the quiet detail that decides whether the answer is right.

Common percentage mistakes

The first mistake is using the new value as the base for percentage change. The original value should be the base when measuring increase or decrease.

The second mistake is thinking a 20 percent increase and a 20 percent decrease cancel each other out. They do not, because the second calculation uses a different base.

The third mistake is confusing percentage and percentage points. Moving from 40 percent to 50 percent is a 10 percentage-point increase, but it is a 25 percent relative increase.

The fourth mistake is forgetting tax or fees after a discount. A discount calculator result may not be the final checkout price if tax, shipping, or service fees apply.

For shopping math, use the Discount Calculator. For tax-inclusive pricing, try the GST Tax Calculator. For business pricing, use the Gross Margin Calculator. For general math, try the Scientific Calculator. You can also browse more Math Academic Calculators.

Percentage Calculator FAQs

What can I calculate with a percentage calculator?

You can calculate percent of a number, what percent one number is of another, percentage increase, percentage decrease, discounts, tips, and reverse percentages.

How do I find 20 percent of a number?

Multiply the number by 20 and divide by 100. For example, 20 percent of 500 is 500 x 20 / 100 = 100.

How do I calculate percentage change?

Subtract the old value from the new value, divide by the old value, then multiply by 100.

What is a reverse percentage?

A reverse percentage works backward from a final value to find the original value before a percentage increase or decrease.

Why do percentage increase and decrease not cancel out?

They use different base values. A 20 percent increase followed by a 20 percent decrease does not return to the original number.

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