Solve everyday percentage problems in one place: find what percent one number is of another, a percent of a number, and the percentage increase or decrease between two numbers.
Percentage Calculator
How the Percentage Calculator Works
Percentages are how everyday life talks about proportions: sale discounts, tips, tax, exam scores, pay rises, interest rates and survey results are all percentages. Underneath, almost every percentage question is one of three questions in disguise, and this calculator is built around exactly those three. It answers “What is X% of Y?”, “X is what percent of Y?”, and “What is the percentage increase or decrease from X to Y?” — each in its own small section, so you only fill in the question you are actually asking.
The formulas are short. A percent of a number is the percent divided by 100, times the number: 15% of 200 is (15 ÷ 100) × 200. A part expressed as a percent is the part divided by the whole, times 100: if 45 out of 180 people agreed, that is (45 ÷ 180) × 100. A percent change is the difference between the new and old values, divided by the starting value, times 100: the starting value is always the base, because the change is measured against where you began. A positive change answer means an increase; a negative one means a decrease.
On this page the three sections work independently — each uses only its own two numbers and ignores the others, so you can answer one question or all three in a single visit. Percentages are entered the way you say them: type 15 for fifteen percent, not 0.15. One built-in limit follows from the maths itself: the “whole” in the second question and the starting value in the third cannot be zero, because dividing by zero is undefined — a part of nothing, or growth from nothing, has no percentage.
How to Use This Calculator
- Decide which of the three questions matches yours: a percent of a number, a part as a percent, or a percent change.
- Find that section on the page and enter its two numbers.
- Press Calculate.
- Read the answer in that section — for a percent change, a minus sign in front means the value went down, not up.
- Repeat with any other section if you have a second question; each one works on its own.
Example
Example 1. What is 15% of 200? Divide the percent by 100: 15 ÷ 100 = 0.15. Multiply by the number: 0.15 × 200 = 30. The answer is 30. The same page’s second section can check a related fact: 45 is what percent of 180? Divide 45 by 180 to get 0.25, times 100 gives 25%.
Example 2. A jacket’s price drops from $80 to $60. What is the percent change? The difference is 60 − 80 = −20. Divide by the starting price: −20 ÷ 80 = −0.25. Times 100 gives −25% — a 25% decrease, which is exactly what a “25% off” label promises.
Common Mistakes to Avoid
The most common percentage error is confusing percentage points with percent. If an interest rate rises from 2% to 3%, that is an increase of one percentage point — but the rate itself has grown by 50%. News reports mix these up constantly; the numbers are not interchangeable. Second, remember that equal up-and-down percentages do not cancel out. Going from 100 up by 25% gives 125, but coming down by 25% from 125 gives 93.75, not 100, because the second percentage is taken from a bigger base. Third, always divide by the original value: for a change, the base is where you started, and for a share, the base is the whole — using the new value or the part instead quietly produces a wrong answer. Fourth, type the percent as you say it (15, not 0.15) in calculators that ask for a percent. Finally, be careful averaging percentages from groups of different sizes: 50% of a class of 10 and 50% of a class of 40 do not combine into a simple average.
Percentage Calculator FAQs
How do I work out the sale price of a discounted item?
Find the discount amount first — for 25% off $80, that is 25% of 80 = $20 — then subtract it from the original price: $60. Or take the shortcut: paying 25% off means paying 75%, and 75% of $80 is also $60.
Which section do I use for a pay rise or a price change?
The third one: percentage increase or decrease. Enter the old value as the start and the new value as the end. A positive result is an increase; a negative result is a decrease.
Can a percentage be more than 100%?
Yes. A part can be bigger than the whole you compare it with — 250 is 125% of 200 — and growth can exceed 100% too, which simply means something has more than doubled.
Why doesn’t a 25% rise followed by a 25% fall get me back to the start?
Because the percentages apply to different bases. The rise is 25% of the smaller starting number; the fall is 25% of the larger number after the rise, so the fall removes more than the rise added.
What does a negative answer mean?
In the change section it means a decrease: −25% is a fall of a quarter. In the “what percent” section a negative answer can only happen if one of your numbers was negative, which is worth double-checking.
Related calculators: Sales Tax Calculator, Interest Calculator, Tip Calculator.