Percentage Calculator
Find X% of a number, percentage increase, percentage decrease, and percent difference — all in one tool.
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Three questions, one tool
Almost every percentage problem is really one of three questions in disguise. What is X percent of Y? Or, X is what percent of Y? Or, by how much did a number go up or down? People mix these up all the time, and the wrong setup gives a number that looks fine but means nothing.
Let's take them one at a time.
The first is the everyday one. You want a slice of a whole. Multiply the whole by the percent, then divide by 100. So 18 percent of 2,000 is 2,000 times 18 divided by 100, which lands at 360. Discounts, GST, tips, marks weightage, it's all this same move.
Second question flips it around. You already have the part and the whole, and you want the percent. Divide the part by the whole, then multiply by 100. Picture a student who scored 425 out of 500. That's 425 divided by 500, which is 0.85, times 100, so 85 percent. Clean.
When something changes
The third question trips up the most people. Percentage change isn't the same as the other two. You take the new value minus the old value, divide that gap by the old value, then multiply by 100. The old number is always what you divide by. Always.
Say onions cost Rs 50 a kilo last month and Rs 65 this month. The change is 65 minus 50, which is 15. Divide 15 by the original 50 and you get 0.3. Times 100, that's a 30 percent increase. If the price had dropped instead, you'd get a negative number, and that just means a decrease.
Here's where folks slip. They divide by the new number, or they divide by the change itself. Both are wrong. Anchor on the starting value and you'll be right every time.
A quick gut check
Before you trust any percentage answer, eyeball it. Is 85 percent of 500 supposed to be more than half? Yes, and 425 is well past 250, so that feels right. Is a jump from 50 to 65 a big one? It's a chunk, and 30 percent sounds about that size. This habit catches typos faster than re-doing the sum.
A few things worth remembering. Percent just means "out of a hundred," nothing fancier. And going up 20 percent then down 20 percent does not bring you back to where you started, because the second 20 percent is taken from a bigger base. Lots of people get burned by that one, especially with salary hikes and investment returns.
Use the calculator above for the arithmetic. But knowing which of the three questions you're actually asking, that's the part that saves you.
Percentage Calculator — frequently asked questions
How do I calculate the percentage of marks I scored?
Divide the marks you got by the total marks, then multiply by 100. If you scored 425 out of 500, that's 425 divided by 500, which equals 0.85, times 100, so 85 percent. The same method works for any exam. Just make sure you use the full maximum marks as the denominator, not some partial total, or the figure will come out wrong.
What is the formula for percentage increase?
Subtract the old value from the new value, divide that difference by the old value, then multiply by 100. So if a price moves from Rs 50 to Rs 65, you do 65 minus 50, which is 15, divided by 50, giving 0.3, times 100, a 30 percent rise. The key thing people forget is to divide by the original number, not the new one.
How do I find what percent one number is of another?
Take the part and divide it by the whole, then multiply by 100. For example, if 30 students out of 120 failed, that's 30 divided by 120, which is 0.25, times 100, so 25 percent. Keep the order straight. The smaller part goes on top and the total goes on the bottom, otherwise your answer flips and stops making sense.
Is a 20 percent increase cancelled by a 20 percent decrease?
No, and this surprises a lot of people. If you start at 100 and add 20 percent you reach 120. Now take 20 percent off 120 and you lose 24, landing at 96, not 100. The decrease is calculated on the larger amount, so it removes more. This is why salary cuts after hikes, or stock drops after gains, often leave you below where you began.
How do I add GST as a percentage to a price?
Multiply the base price by the GST rate and divide by 100 to get the tax, then add it back. On a Rs 2,000 item at 18 percent GST, the tax is 2,000 times 18 divided by 100, which is 360. Your final price becomes 2,360. To go the other way and strip GST out of an inclusive price needs a different formula, so check whether your price already includes tax first.
Why do I get different answers depending on which number I divide by?
Because the question itself changes. Finding a percent of a number, finding what percent one is of another, and finding a percentage change are three separate calculations with different denominators. The first multiplies, the second divides the part by the whole, the third divides the change by the original value. Decide which question you are actually asking before you pick the formula, and the confusion clears up.
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