How do I calculate 15% of 240?

Use the "Percent of a Number" block. Enter 15 as the percent and 240 as the number. The formula is (15 / 100) × 240 = 36. The general rule is to divide the percent by 100 to turn it into a fraction, then multiply by the number.

How do I find what percentage one number is of another?

Use the "Part of Whole" block. Enter the part and the whole, and the formula is (part / whole) × 100. For example, 45 out of 300 is (45 / 300) × 100 = 15%. If the whole is zero the answer is undefined — you cannot take a percentage of nothing — so the tool shows a dash rather than a misleading number.

What is the difference between "percentage change" and "increase/decrease"?

They run in opposite directions. Percentage change starts from two known values (old and new) and tells you the percent between them. Increase/decrease starts from one value and a percent, and tells you the resulting value. Use the first to measure a change that already happened, and the second to apply a markup, discount, raise, or reduction you are planning.

Can I use this for marks, discounts, and growth checks?

Yes — it is built for exactly that everyday mix. For a shop discount use increase/decrease; to see how much your marks improved use percentage change; to find your score as a percentage use part of whole. For exam-specific target marks, the separate Percentage & Marks Calculator is purpose-built.

Student Tool

Percentage Calculator

Four percentage calculators in one: percent of a number, what percent one value is of another, percentage change between two values, and increasing or decreasing a number by a percent. Each shows its formula and result.

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Percent of a Number

PercentofNumber

15% of 240

Formula: (15 / 100) x 240

Part of Whole

PartofWhole

45 is what percent of 300?

15%

Formula: (45 / 300) x 100

Percentage Change

Old ValueNew Value

Difference: 160 (increase)

20%

Formula: (new - old) / |old| x 100

Increase or Decrease

Starting NumberPercent

Change amount: 150

1,400

Formula: number + (number x percent / 100)

Common Percentage Formulas

Percent of value

(percent / 100) x value

Part as percent

(part / whole) x 100

Percentage change

((new - old) / |old|) x 100

Increase/decrease

value +/- (value x percent / 100)

Four questions, four blocks — the trick is picking the right one

Almost every percentage problem is one of four questions, and the mistakes people make are almost never arithmetic — they are picking the wrong question. A percent is just a number written out of 100, so 15% is the fraction 15/100, or 0.15. Once you know which of the four situations you are in, the formula follows and the answer is a single multiplication or division.

The four are laid out as separate blocks above so you never have to rearrange a formula. Finding a slice of a value (“15% of 240”) is percent of a number. Turning a part and a total into a percent (“45 out of 300”) is part of whole. Comparing a before and an after (“800 rose to 960”) is percentage change. Applying a markup or discount to a starting figure (“1250 plus 12%”) is increase or decrease. Each block prints the exact formula next to its result, so the answer is always checkable rather than a black box.

Percentage change is not symmetric

The most counter-intuitive thing about percentages is that a rise and the matching fall are not the same percent, because the base changes underneath you.

100 up to 150 is a 50% increase (50 out of 100).
150 back down to 100 is only a 33.3% decrease (50 out of 150).
A price cut of 20% followed by a 20% rise does not return to the original — it lands 4% lower.

This is why the change block always divides by the old value: the starting point is the base, and reversing the direction reverses which number that is.

Percentage points are not percent

A second common trap is confusing a change in percent with a percent change of a percent. If an interest rate goes from 4% to 6%, that is a rise of 2 percentage points, but a 50% increasein the rate itself.

Both statements are true and they describe the same move; they just measure it differently. When a figure is itself a percentage — a rate, a share, an attendance figure — be clear about which one you mean, because the two numbers can differ wildly and headlines often pick whichever sounds bigger.

Rounding, and what the tool leaves to you

Results are shown to a few decimal places and grouped with commas for readability, which means a long repeating decimal like 33.333…% is displayed rounded. For most purposes that is exactly what you want, but if you are chaining several percentage steps together, round only at the very end — rounding at each step lets small errors accumulate. When a figure has to match an official total to the last paisa or cent, treat this as the check and the source document as the authority.

Note: These are arithmetic results, computed on your device and never uploaded. Tax, billing, and grading systems apply their own rounding and rules, so verify against the official bill, marksheet, or statement before making a decision that depends on the exact figure.

How to Use

Pick the block that matches your question — the four cover almost every percentage problem.

Enter the values for that block; the formula and result update as you type.

Read the result with its formula shown beside it, and copy the value when you need it.

Features

Percent of a number — find a slice of a value

Part of whole — find what percent one number is of another

Percentage change — compare an old and new value, with a signed result

Increase or decrease a number by a chosen percent

Every result shows the formula it used, so the answer is checkable

Runs entirely in your browser — nothing you type is uploaded

Common Questions

Percentage change always measures growth relative to the starting point, so the old value is the base: (new − old) / |old| × 100. Dividing by the new value instead answers a different question and gives a different number. This tool uses the absolute value of the old number as the base so that a rise always reads as positive and a fall as negative, even when the starting value is negative. Note that percentage change is not symmetric — going from 100 to 150 is a 50% increase, but 150 back to 100 is only a 33.3% decrease, because the base changed.

About Percentage Calculator

Solve everyday percentage math in one place. Find what a percent of a number equals, calculate what percent one value is of another, compare old and new values with a signed percentage change, and increase or decrease any number by a chosen percentage. Each of the four blocks shows the exact formula next to its result, and undefined cases like a zero base are shown as a dash rather than a misleading number.

Also known as: calculate percentage, percent calculator, what percent, percent of a number, percentage increase calculator, percentage decrease calculator, percent change calculator, what percent is x of y, percentage difference, add percent to number.