The Percentage Change Calculator (% change calculator) will quantify the change from one number to another and express the change as an increase or decrease. 
This is a % change calculator.  From 10 apples to 20 apples is a 100% increase (change) in the number of apples.
This calculator will be most commonly used when there is an “old” and “new” number or an “initial” and “final” value. A positive change is expressed as an increase amount of the percentage value while a negative change is expressed as a decrease amount of the absolute value of the percentage value.
You will generally use the percent change calculation when the order of the numbers does matter; you have starting and ending values or an "old number" and a "new number." When you are just comparing 2 numbers you may want to use the percent difference formula and calculation. 
Related calculations can be done with Percentage Calculator and conversions can be solved with Decimal to Percent, Percent to Decimal, Fraction to Percent, or Percent to Fraction.

percentage change = (Valnew - Valold) / Valold × 100%