Percentage Calculator

ABOUT THIS TOOL

Calculate what percentage one number is of another, find the percent change between two values (like a price before and after a sale), or determine the percent difference between two figures. The tool handles the three most common percentage questions people run into day to day, without requiring you to remember which formula applies to which situation. Students use it to check grading math, shoppers use it to verify discounts and markups, and analysts use it to track how a metric moved between two periods. Because percent change and percent difference are calculated differently — one has a clear starting point, the other doesn't — the calculator keeps them separate so you get the right number.

HOW TO USE

1. Pick the calculation you need: percentage of a number, percent change, or percent difference.
2. Enter the two values relevant to that calculation.
3. Read the result, shown as a percentage.
4. For percent change, note whether the result is an increase or a decrease.
5. Repeat with new numbers to check multiple scenarios quickly.

COMMON USE CASES

• A shopper checking whether a sale price actually reflects the advertised 30% discount.
• A student calculating a test score from points earned out of total points.
• A manager comparing this quarter's sales to last quarter's to report the percent change.
• Someone calculating a tip or commission based on a percentage of a total.
• An analyst comparing two survey results to find the percent difference between them.

TIPS & COMMON MISTAKES

• Percent change and percent difference are not the same thing — percent change assumes a clear before and after, while percent difference treats both values neutrally.
• A percent increase and the percent decrease that undoes it are not equal — increasing $100 by 50% gives $150, but decreasing $150 by 50% gives $75, not $100.
• Watch decimal placement: 5% is 0.05, not 5, when used in other formulas.
• For discounts, remember the percentage applies to the original price, not the sale price, unless stated otherwise.

MORE QUESTIONS

What's the difference between percent change and percent difference?

Percent change measures the change from a specific starting value to an ending value, so the order of the numbers matters. Percent difference treats the two values symmetrically and is often used when neither number is clearly the 'original.'

Why don't equal percentage increases and decreases cancel out?

Because each percentage is calculated on a different base. A 20% increase on 100 gives 120, but a 20% decrease on 120 gives 96, not 100, since the second calculation is based on the larger number.

How do I calculate a percentage of a percentage?

Convert each percentage to a decimal and multiply them together, then convert back — for example, 50% of 20% is 0.5 × 0.20 = 0.10, or 10%, not the two percentages added together.

Can percent change be negative?

Yes. A negative percent change simply indicates a decrease from the starting value; the calculator shows the sign so you can tell an increase from a decrease at a glance.

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