Calculate the percentage change from one number to another and express the change as an increase or decrease. 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 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.
Percentage change equals the change in value divided by the absolute value of the original value, multiplied by 100.
Percentage change = ( ΔV / |V1| ) * 100 = ((V2 - V1) / |V1|) * 100
For example one, to calculate the percentage change:
Saying a -25% change is equivalent to stating a 25% decrease.
Note that if we let V1 = 2.625 and V2 = 3.50 we would get a 33.3333% increase. This is because these percentages refer to different amounts. 25% of 3.50 and 33.3333% of 2.625. Both are equal to our difference of 0.875.
As a second example let's look at a change that includes negative numbers and taking the absolute value of V1 in the denominator makes a difference.
Saying a 200% change is equivalent to stating a 200% increase.
As a third and final example let's look at another change that includes negative numbers and taking the absolute value of V1 in the denominator makes a difference.
Saying a -100% change is equivalent to stating a 100% decrease.
Wikipedia contributors. "Percent difference: percent change" Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, last visited 18 Feb. 2011.
Percent Change, Increase, Difference from Dr. Math, last visited 22, Feb. 2011.