Percentage Calculator

Three calculators in one: find what X% of a number is, discover what percentage one number is of another, and measure the percent increase or decrease between two values.

How much is X% of Y?

Result: —

X is what percent of Y?

X is: —

Change from A to B

Change: —

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  1. Pick the block that matches your question — each one calculates as you type.
  2. First block: how much is 15% of 200? (answer: 30).
  3. Second block: 30 is what percent of 200? (answer: 15%).
  4. Third block: from 200 to 230, what is the change? (answer: +15%).

The three everyday percentage problems

Almost every percentage question fits one of three shapes. "How much is X% of Y" multiplies the value by the rate: 15% of 200 = 200 × 0.15 = 30 — this is the discount-and-tip calculation. "X is what percent of Y" divides the part by the whole: 30 ÷ 200 = 0.15 = 15% — the one for test scores and market share. And "change from A to B" compares two moments: (B − A) ÷ A — the shape used for price increases, salary raises and investment returns.

The classic trap: percentage points vs. percent change

Going from 10% to 15% is an increase of 5 percentage points, but a 50% relative increase. News and contracts mix these up all the time. Another trap: a 50% drop followed by a 50% rise does not return to the start (100 → 50 → 75), because the second percentage applies to a smaller base.

Quick mental math tricks

10% is just moving the decimal point (10% of 340 = 34). 5% is half of that. 15% = 10% + 5%. 1% is two decimal moves. And X% of Y always equals Y% of X — 8% of 25 sounds hard, but 25% of 8 is obviously 2.

Frequently asked questions

How do I calculate a discount?

Use the first block: enter the discount rate and the price. 20% off a $150 item = $30 off, so you pay $120.

How do I find the percent change between two values?

Use the third block: (final − initial) ÷ initial × 100. From 80 to 100 it is +25%; from 100 to 80 it is −20%. The direction matters because the base changes.

What is the difference between percentage points and percent?

From 10% to 12% is +2 percentage points, but a +20% relative change. Interest rates use points; growth comparisons use percent.

Why does −50% then +50% not get back to the start?

Because the second percentage applies to the reduced value: 100 − 50% = 50, and 50 + 50% = 75. To undo a 50% drop you need +100%.

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