Formula & assumptions
Part = base × percent/100; change = (new − original)/original × 100
The three modes answer different questions: a percentage of a quantity, a quantity’s share of a base, and a change relative to the original. The base is always the first field. Percentage change is different from percentage-point change: moving from 20% to 25% is five percentage points but a 25% relative increase.
Worked example
EXAMPLE
20% of 100 is 20. A rise from 80 to 100 is (100−80)/80 × 100 = 25%, while a fall from 100 to 80 is −20%.
How to use this calculator
- Choose the question you want to answer.
- Enter the base or original value first, then the percentage or comparison value.
- Read the formula to verify which denominator was used.
Frequently asked questions
Why are the increase and decrease different?
They use different original values as denominators. Returning to the starting price does not require the same percentage.
Can I calculate growth from zero?
No. A percentage change with a zero original value is undefined. Use the absolute difference instead.
Can the result exceed 100%?
Yes. A comparison value can exceed its base, and growth can exceed the original amount.