Reference formulas and worked examples below keep their stated units. Monetary examples use USD; dimensional examples use US customary units unless labeled otherwise. Metric calculator inputs are converted to these reference units before calculation. Choosing another currency does not convert example amounts or exchange money.
How to use this percentage calculator
Choose a calculation type, then enter the two values. Field labels change to match your question.
How the calculation works
Percent of a number = percentage ÷ 100 × number. A part as a percentage = part ÷ whole × 100.
Percentage change = (new − original) ÷ original × 100. A positive answer is an increase; a negative answer is a decrease. This mode requires a positive original value.
Percentage difference uses |A − B| ÷ [(A + B) ÷ 2] × 100. It is symmetric, accepts nonnegative values, and is undefined when both are zero.
To increase or decrease a starting value by p%, multiply it by (1 + p ÷ 100) or (1 − p ÷ 100). Results are displayed to at most six decimal places.
Worked example
15% of 200 is 15 ÷ 100 × 200 = 30. Going from 200 to 230 is a 15% increase. Taking 15% off 200 gives 170.
Limits and assumptions
Uses ordinary decimal arithmetic. A percentage relative to zero is undefined. Percentage change from a negative starting value is excluded because its interpretation is ambiguous.
Frequently asked questions
What is the difference between percent change and percentage points?
A rate changing from 10% to 15% rises by 5 percentage points. Relative to the original rate, it rises by 50%.
Can I calculate a discount?
Choose Decrease X by Y%, enter the original price as X and discount percentage as Y.
Can I enter decimals or negative values?
Yes. Decimal and signed values are accepted, except the original value in percentage-change mode must be positive.