How to use it
Enter a percentage and the starting value, then choose Calculate. Enter 15 to mean 15%. The result retains the starting value’s unit, whether that is pounds, metres or a count.
Method and example
Use amount = percentage ÷ 100 × value.
For 15% of 200, the calculation is 15 ÷ 100 × 200 = 30. A 15% reduction on a £200 purchase therefore saves £30, leaving £170 before any additional charges. Enter the displayed price as the base; the calculator does not decide which charges belong in that price.
Assumptions and limits
This calculation finds a percentage of one value. Comparing an old value with a new one or calculating compound growth requires a different formula. Zero percent gives zero; percentages above 100 and negative percentages are allowed. Keep the base consistent when comparing percentages.
The percentage can range from −1,000,000 to 1,000,000, and the starting value from −1,000,000,000,000 to 1,000,000,000,000. Enter plain decimal numbers without grouping commas.
Numbers shown on screen may be rounded. The calculator does not implement UK VAT, accounting or lender-specific rounding rules. NIST’s guide, section 7.10.2 explains the mathematical percent symbol; the calculation itself is independent of currency and market.