Math ToolMulti-Directional

Percentage Calculator

Calculate percentages of numbers, percentage increases, discounts, fractional shares, and reverse percentages with step-by-step arithmetic.

Select Calculation Type

%
15% of 200
30
Formula: (15 ÷ 100) × 200 = 30

Mental Math Percentage Shortcuts

  • 10% of any number: Move the decimal point one place to the left.
  • 5% of any number: Take 10% and divide by 2.
  • 15% of any number: Take 10% and add 5% (ideal for restaurant tipping).
  • Percentages are reversible: 8% of 50 is identical to 50% of 8 (= 4).

Core Percentage Formulas

1. Percentage of a Value:
P = (X / 100) × Y
2. Percentage Increase / Decrease:
% Change = [ (Final − Initial) / Initial ] × 100
3. Reverse Percentage:
Original Value = Amount / (Percentage / 100)

Frequently Asked Questions

How do you calculate the percentage of a number?

To find X% of Y, convert the percentage into a decimal by dividing by 100, then multiply by the total number: (X ÷ 100) × Y. For example, 15% of 200 is: 0.15 × 200 = 30.

How do you calculate percentage increase or change between two numbers?

Subtract the starting value from the new value, divide by the absolute value of the starting number, and multiply by 100: [(New − Old) ÷ Old] × 100. If positive, it is a percentage increase; if negative, a percentage decrease.

What is a reverse percentage and how is it calculated?

Reverse percentage is finding the original amount before a percentage was taken. If $30 represents 25% of a total, divide the part by the percentage in decimal form: 30 ÷ 0.25 = 120.

Related Mathematical & Financial Calculators