Percentage formulas
Part = percent ÷ 100 × whole. Percent = part ÷ whole × 100. Percent change = (new − old) ÷ old × 100. A change from 80 to 100 is +25%.
Worked example
15% of $80 is $12. 12 is 15% of 80. A price that moves from $80 to $100 is a 25% increase: (100 − 80) ÷ 80.
A 25% decrease from $100 is $75, which is not the reverse of a 25% increase. To undo a 25% increase you divide by 1.25, not subtract 25%.
Common questions
Why is percent change different from percent of?
Percent of compares a piece to a whole. Percent change compares a new value to an old value.
Can the result be over 100%?
Yes. 40 is 200% of 20. A jump from 10 to 30 is a 200% increase.