How do I calculate percentage increase between two numbers?

Subtract the old value from the new value, divide that difference by the old value, and multiply by 100. For example, growing from 80 to 100 is ((100 - 80) ÷ 80) × 100 = +25%.

Why does a 20% increase followed by a 20% decrease not return to the original number?

Because the 20% decrease applies to the larger increased number. Starting at 100: +20% gives 120, and -20% of 120 subtracts 24, leaving 96.

Instant Percentage, Discount & Change Calculator

Solve "X% of Y", "X is what % of Y", percentage change & discounts in real time.

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1. What is X% of Y?

What is % of

(20 ÷ 100) × 250

2. X is what % of Y?

is what % of

(45 ÷ 180) × 100

3. Percentage Increase / Decrease

From to

((108 − 80) ÷ 80) × 100

4. Sale Discount or Markup

Difference: 18

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How to Use Instant Percentage, Discount & Change Calculator

Type numbers into any of the four instant calculators: "What is X% of Y?", "X is what % of Y?", "Percentage Change from X to Y", or "Add / Subtract X%".
Results update as you type with the exact formula and step-by-step working shown underneath.
Click any result pill to copy the number to your clipboard.

Four Essential Percentage Formulas Used Every Day

What is X% of Y? Result = (X ÷ 100) × Y
X is what % of Y? Percentage = (X ÷ Y) × 100
Percentage Change (from A to B): Change % = ((B − A) ÷ |A|) × 100
Discount / Markup (Y ± X%): Final = Y × (1 ± X ÷ 100)