Percentage Calculator Calculate a percent of a value before and after, or find the percentage change between two values, and see how to calculate each one. Examples: Apply 10% to 100, and see how each value was calculated Try 12.5% of 50: the "50 less 12.5%" value is 43.75. Then try 12.5% of 43.75 (shows that before a 12.5% reduction it was 50.)