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Percentage Calculator

Solve any percentage problem instantly. Find discounts, markups, and calculate growth.

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What is X% of Y?

What is
% of
?
30

X is what % of Y?

is what % of
?
20 %

Percentage Increase/Decrease

From
to
is a
+50 %Increase

The Mathematics of Everyday Life

Percentages are simply fractions out of 100. While the concept is simple, manually applying percentage formulas to real-world scenarios—like retail discounts or stock market losses—can be frustrating.

How to Use This Tool

  1. Step 1: Choose Scenario - Select the type of percentage problem (e.g., finding a discount or % change).
  2. Step 2: Enter Numeric Data - Input your values into the labeled fields for instant calculation.
  3. Step 3: Understand Logic - Read the clear explanation of how the result was derived mathematically.

Deeper Dive

Want to master the formulas behind percentages and discounts?

Read our guide on the three percentage problems

How the percentage calculator works

The calculator has three modes. What is X% of Y multiplies Y by X divided by 100. X is what % of Y divides X by Y and multiplies by 100. Percentage change subtracts the old value from the new one, divides by the old value and multiplies by 100. A negative result means a decrease.

A percentage is always relative to a starting amount. Changing which number you treat as the starting point changes the answer, which is the source of most percentage mistakes.

Worked examples

What is 15% of 80?

  • 80 × 15 ÷ 100 = 12

30 is what percent of 120?

  • 30 ÷ 120 × 100 = 25%

Percentage change, up and down

  • From 80 to 100: (100 − 80) ÷ 80 × 100 = +25%
  • From 100 back to 80: (80 − 100) ÷ 100 × 100 = −20%
  • The same 20-unit gap is a 25% rise one way and a 20% fall the other, because the starting amounts differ.

Tips and common mistakes

  • Two discounts do not add up. A 20% discount followed by a further 10% discount leaves 0.8 × 0.9 = 0.72 of the price, a 28% saving in total, not 30%.
  • Do not mix up percent and percentage points. If an interest rate moves from 4% to 5%, it rose by 1 percentage point but by 25% in relative terms.
  • To add a percentage, multiply by 1 plus the rate: adding 15% to 200 is 200 × 1.15 = 230.

Frequently Asked Questions

To calculate X% of Y, you divide the percentage (X) by 100, and then multiply that number by the total value (Y). For example, to find 20% of 150: (20 / 100) * 150 = 30.
To find the percentage change between two numbers, subtract the Old Number from the New Number. Then divide that result by the Old Number. Multiply the final result by 100. If the answer is positive, it's a percentage increase. If it's negative, it's a decrease.
Percentages are the foundation of all finance. Interest rates on your bank account, the APR on your credit card, and the ROI (Return on Investment) of your stock portfolio are all expressed as percentages.

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