# How to Calculate Increase & Decrease

by Bradley James Bryant ; Updated September 11, 2015Data analysts are always looking for better ways to explain trends. The better you can explain what's going on with the data, the more people can use the data to make better and more informed decisions. One of the most common ways to analyze data is to calculate the percentage increase or decrease. An increase is considered a positive change in values, and a decrease is considered a negative change in value. The answer is generally expressed in percentage terms for easier comparison.

Determine the starting value. This is also referred to as the initial value. For instance, let's say you are analyzing a stock and the initial value of XYZ stock is $50.

Calculate the increase or decrease in value. This is the change in value from Day 1 to the next day in which the value is taken. For instance, if the stock falls to $45 on Day 2, the change in value is calculated by taking the difference between Day 1 and Day 2. The calculation is: $45 - $50 = -$5. However, if the stock increases to $55 on Day 2, the calculation is: $55 - $50 = $5.

Calculate the percentage increase and decrease. The percentage is calculated by dividing the change in value by the starting value. For instance, if you want to calculate the percentage change in value for the stock from Day 1 to Day 2 the calculation is: $5 / $50 = .1 or 10 percent. This translates into a positive 10 percent change if the value increases, and a negative 10 percent change if the value decreases.

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