IconVault's Percentage Calculator handles the three percentage questions people actually ask, with live results as you type. X% of Y finds a share of a value, X is what % of Y turns a part and whole into a percent, and Percent change shows increase or decrease between an old and a new value with the direction labeled.

It is free and runs fully in your browser, and you can copy the result to your clipboard in one click. Built-in examples cover the everyday cases: discounts (what is 25% off 80), tips and tax (adding 18% to a bill), and growth (from 200 to 260 is a +30% change). The honest note: results are rounded to four decimal places and formatted for readability, so for high-precision engineering math verify in your own tooling.