% Percentage Calculator

Three common percentage problems, each calculated live as you type.

What is X% of Y?

Percent

X is what percent of Y?

Percentage change from X to Y

From (X)

To (Y)

The three calculations

X% of Y            = (X / 100) x Y
X is what % of Y   = (X / Y) x 100
change from X to Y = ((Y - X) / |X|) x 100

The loaded defaults show all three agreeing: 15% of 200 is 30, 30 is 15% of 200, and 80 rising to 100 is a 25% increase. Results are rounded to four decimal places, so a third of a number shows as 33.3333%. The change box uses the absolute value of the starting number, which keeps the sign sensible when you start from a negative figure such as a loss of 40 moving to a profit of 20.

The same gap, two different percentages

Percentage change is not symmetric, because the starting number is the denominator and it changes when you swap the direction:

80 to 100 is +25%, since the 20 gained is a quarter of 80.
100 back to 80 is -20%, since the same 20 is a fifth of 100.
A 25% rise then a 25% fall does not return you to the start: 80 becomes 100 becomes 75.

Watch the difference between percent and percentage points. A savings rate going from 4% to 5% is a rise of one percentage point, but the middle box calls it a 25% increase. Both are correct; headlines pick whichever sounds bigger.

Frequently asked questions

What is 15 percent of 200?

30. Multiply 200 by 0.15, or take 10% (20) and half of that (10) and add them. The same trick handles most mental percentage work: 15% of a $48 bill is $4.80 plus $2.40, so $7.20.

How do I work out percentage increase?

Subtract the old value from the new one, divide by the old value, then multiply by 100. From 80 to 100 that is 20 / 80 x 100, which is 25%.

Why can a percentage change be more than 100%?

Because the change is measured against the starting value, not against a ceiling. Going from 80 to 200 is a 150% increase - you added one and a half times what you began with. A decrease, by contrast, cannot pass -100% unless the value goes negative.