What is the percentage increase/decrease from to? %. Tips: Use tab to move to the next field. Use shift-tab to move to the previous field. Press enter to calculate. Also, other percentage and percent calculators that are often needed. Percentage Calculator see examples Add or Subtract a Percentage see examples. Add or Subtract a Percentage · See examples · Percent Calculator · Percent Change. How to add or subtract percentages. If your calculator does not have a percent key and you want to add a percentage to a number multiply that number by 1 plus.