Percentage Calculator

To find X percent of Y, multiply Y by X and then divide by 100. The formula is: result = Y × X ÷ 100. For example, to find 15% of 200, compute 200 × 15 ÷ 100, which equals 30. This is the most common percentage calculation and appears in everyday situations like figuring out a discount on a product, computing sales tax, or determining a tip. The first calculator card on this page automates this formula for you. Simply type the percentage in the first field and the number in the second field, and the result appears instantly. You can change either value at any time and the answer updates in real time, making it easy to compare different percentages or test multiple scenarios without restarting the calculation.

To determine what percentage a part is of a whole, divide the part by the whole and multiply by 100. The formula is: percentage = (part ÷ whole) × 100. For instance, if you scored 42 out of 60 on a test, divide 42 by 60 to get 0.7, then multiply by 100 to find that you scored 70%. This calculation is useful for grade percentages, completion rates, market share analysis, and any time you need to express a ratio as a percentage. The second card on this page handles this calculation. Enter the part value in the first field and the whole value in the second field. The percentage result updates live as you type, and you can copy it with a single click.

Percentage change measures how much a value has increased or decreased relative to its original amount. The formula is: percentage change = ((new value − old value) ÷ old value) × 100. If the result is positive, the value increased. If the result is negative, the value decreased. For example, if a stock price went from $80 to $100, the change is ((100 − 80) ÷ 80) × 100 = 25%, which is a 25% increase. If the price dropped from $100 to $80, the change is ((80 − 100) ÷ 100) × 100 = −20%, which is a 20% decrease. The third calculator card on this page computes this automatically and shows a color-coded badge indicating whether the change is an increase, a decrease, or zero.

The reverse percentage formula lets you find the original base number when you know a value and the percentage it represents. If X is Y% of some unknown number, the formula is: base = X ÷ Y × 100. For example, if a store says you saved $45 and that was 30% off the original price, the original price was 45 ÷ 30 × 100 = $150. This formula is valuable for back-calculating original prices from discounts, finding total populations from sample percentages, or determining full quantities when only a fraction is given. The fourth calculator card handles this automatically. Enter the known value and the percentage, and the base number appears immediately.

To convert a percentage to a fraction, write the percentage over 100 and simplify. For example, 75% becomes 75/100, which simplifies to 3/4 by dividing both the numerator and the denominator by their greatest common divisor (25 in this case). For repeating decimals like 33.33%, the closest simple fraction is 1/3. The converter at the bottom of the tool area does this simplification for you. Type any percentage value and it will show the decimal equivalent, the simplified fraction, and the ratio form. This is helpful for cooking recipes, probability problems, and academic work where fractions are preferred over percentages.

One of the most frequent mistakes is confusing the base when calculating percentage change. Always divide by the original value, not the new value, when determining how much something has increased or decreased. Another common error is thinking that a 50% increase followed by a 50% decrease returns you to the starting number. In reality, if you start at 100, a 50% increase brings you to 150, and a 50% decrease of 150 brings you to 75, not 100. A third pitfall is adding percentages of different bases as if they were absolute numbers. For instance, 10% of 200 and 10% of 300 are different amounts (20 and 30), so combining them requires working with the actual values rather than the percentages. This calculator helps you avoid these errors by computing exact results so you never have to rely on mental math shortcuts that can lead to mistakes.

Yes, this tool is completely free with no account required and no usage limits. All calculations run entirely in your browser using JavaScript, which means nothing is sent to a server and your data stays private on your device. You can use it on any device with a web browser, including smartphones, tablets, laptops, and desktops. Bookmark this page for quick access whenever you need percentage calculations for school, work, shopping, or personal finance. The tool works offline after the initial page load since all the math happens locally in your browser without requiring an internet connection for subsequent calculations.