Solve any percentage problem instantly
Percentages are everywhere in daily life — discounts, tips, taxes, interest, exam scores, statistics — yet the formulas are easy to forget under pressure. This free percentage calculator handles the three questions people ask most: what is a percentage of a number, what percent one number is of another, and the percentage increase or decrease between two values. Every answer updates live as you type, so you spend no time remembering formulas and no time reaching for a separate calculator.
The three calculators explained
- Percentage of a number. Answers questions like "what is 15% of 200?" This is the one you use for discounts, tips, tax, commission and interest.
- Percentage ratio. Answers "30 is what percent of 150?" Perfect for turning a score or a part into a proportion of the whole.
- Percentage change. Answers "what is the change from 120 to 150?" Ideal for measuring growth, decline, price movements and results over time.
The formulas behind the buttons
Understanding the maths makes it easy to check your own work and to teach the concept to others. To find a part, use part = (percent ÷ 100) × whole. To find a percentage, use percent = (part ÷ whole) × 100. To find a change, use change = ((new − old) ÷ old) × 100, where a positive result is an increase and a negative one is a decrease. These three simple relationships cover the vast majority of real-world percentage problems you will ever face.
Everyday examples
Consider how often percentages appear in an ordinary week. A shop advertises 20% off, and you want the final price. A restaurant bill needs a 15% tip. Your salary rises by 5%, and you want the new figure. An exam is marked 46 out of 60, and you want the percentage. A stock or a subscription price changes, and you want to know by how much. Each of these maps onto one of the three calculators here, turning a moment of mental arithmetic into an instant, reliable answer.
Why percentages confuse people
Percentages trip people up mainly because the same word describes several different operations. "20% off" (a percentage of a number) is not the same calculation as "sales rose 20%" (a percentage change), even though both use "20%". A classic pitfall is percentage change in reverse: if a price rises 20% and then falls 20%, you do not end up back where you started, because the second 20% is taken from a larger number. Seeing each type of problem in its own clearly labelled calculator removes that confusion and helps the underlying logic click.
How to use the tool
Just type your numbers into whichever of the three calculators matches your question. There is no submit button — results appear immediately and update as you edit, so you can experiment freely. Want to see how a bigger discount changes the price, or how a different starting figure affects a percentage change? Adjust the inputs and watch the answer move. Because everything runs in your browser, it is fast, private and always available. Whether you are shopping, budgeting, studying or working, this calculator takes the guesswork out of percentages.
Reverse percentages and a common trap
One area where people slip up is the reverse percentage — working backwards from a figure that already includes a change. Suppose an item costs 120 after a 20% discount, and you want the original price. It is tempting to add 20% to 120, but that gives the wrong answer, because the 20% was taken from the larger original, not from 120. The correct approach is to recognise that 120 represents 80% of the original, so you divide 120 by 0.8 to get 150. The same logic applies to tax: if a total of 110 includes 10% tax, the pre-tax amount is 110 divided by 1.1, which is 100, not 99. Another classic trap is assuming that a percentage rise and an equal percentage fall cancel out — they do not. A price that goes up 20% and then down 20% ends up lower than it started, because the second percentage is calculated from a bigger number. Keeping these two pitfalls in mind, and using the calculators above to check your working, will save you from the most common percentage mistakes.
Frequently asked questions
How do I find a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of 200 is (15 ÷ 100) × 200 = 30. The first calculator does this instantly.
How do I find what percent one number is of another?
Divide the first number by the second and multiply by 100. For example, 30 out of 150 is (30 ÷ 150) × 100 = 20%.
How is percentage change calculated?
Subtract the old value from the new value, divide by the old value, and multiply by 100. A rise from 120 to 150 is a 25% increase.
Can I use it for discounts and tips?
Yes. For a sale price, calculate the discount as a percentage of the original and subtract it. The same first calculator handles tips on a bill.