Percentage Calculator — % of, Change, Increase & Decrease

Percentage Calculator

Percentage Calculator covers five operations: finding what X% of a number is, finding what percent one number is of another, finding the percentage increase or decrease between two numbers, and increasing or decreasing a number by a percentage. Enter two values, pick a mode, and the result appears, with an increase or decrease label shown where it applies.

How each mode is calculated

Finding X% of a number multiplies the number by X and divides by 100. Finding what percent one number is of another divides the first number by the second and multiplies by 100. The percentage change between two numbers takes their difference, divides it by the starting number, and multiplies by 100, using the absolute value and labeling the result as an increase or a decrease depending on the sign of that difference. Increasing a number by a percentage multiplies it by 1 plus that percentage as a decimal; decreasing it multiplies by 1 minus that percentage as a decimal. Every result is rounded to two decimal places before it's displayed.

Concrete use cases

Working out a tip on a restaurant bill, checking how much a discount actually takes off a price, comparing a subscription price before and after it changes, or estimating a raise are the same X%-of-Y or percentage-change calculation with different numbers plugged in.

Worked examples

A $65 jacket marked down by 20% comes to $65 * (1 - 20/100) = $52 using the decrease-by-percentage mode. A streaming subscription that went from $40 to $52 a month is a $12 difference, and (12 / 40) * 100 = 30% — a 30% increase, not a decrease, since the price went up.

Formulas and common values

The five formulas behind each mode, followed by common percentages of $80 as a quick reference:

X% of Y = (X * Y) / 100
X is what % of Y = (X / Y) * 100
% change from X to Y = |(Y - X) / X| * 100
Increase X by Y% = X * (1 + Y / 100)
Decrease X by Y% = X * (1 - Y / 100)