How to use it
Enter the percentage and the starting value, then select Calculate. For 15%, enter 15, not 0.15. The result uses the same unit as the starting value: a percentage of 200 dollars is an amount in dollars.
Method and example
The calculation is amount = percentage ÷ 100 × value.
For 15% of 200, divide 15 by 100 to get 0.15, then multiply by 200. The result is 30. If a $200 item has a 15% discount, the discount is $30; subtract it from the original price to get $170 before any other charges.
Assumptions and limits
This calculation finds a share of one value. Percentage change and compound growth use different formulas. Zero percent produces zero. A percentage over 100 can produce an amount greater than the starting value; a negative percentage changes its sign. Use the same base value when comparing results.
The percentage must be between −1,000,000 and 1,000,000; the value must be between −1,000,000,000,000 and 1,000,000,000,000. Enter plain decimal numbers without grouping commas.
Displayed decimals may be rounded. This general number calculation does not apply bank, tax, or invoice rounding rules. The NIST guide, section 7.10.2 describes percent as a representation of the number 0.01.