Definition
Percent increase
An increase compared with the original value and written as a percent.
What it means
Find the extra amount, then compare that extra with the starting amount. The same increase can make different percents when the starting values are different.
Remember it
Extra ÷ start × 100%.
Example
A tank rises from 80 litres to 100 litres. The increase is 20 litres, and 20 ÷ 80 = 0.25, so the amount has a 25% increase.
Watch for
Use percent increase only when the new value is larger than a positive original value. Starting from zero makes the usual formula undefined.
Common mix-up
The percent is not found by dividing the increase by the new value. The comparison is always with the original value.
Exact meaning
For a positive starting value and a larger new value, percent increase is (new − starting) ÷ starting × 100%. The starting amount supplies the denominator.