Calculating Percent Change

The Percent Change Equation

When you go shopping on Black Friday and Cyber Monday, you’ll probably see coupons like “$50\%$ off select items!” or “$25\%$ off your entire order!”

These coupons are examples of percent change. We use percent change when an increase or decrease in value is based on the starting, or initial, value.

50% off tells us that if the initial value is $100, the final value is $50, which is a decrease of $50. If the initial value is $200, the final value is $100, which is a decrease of $100. The value of the decrease isn't always the same, but the percent decrease does stay the same.

The following fraction gives us the portion of the initial value that changed:

We know we need to multiply decimals by $100$ to change them to percents, so the percent change formula is equal to:

Percent change can be positive or negative. If our final value is bigger than our initial value, then we have a percent increase, and our percent change is positive.

If our final value is smaller than our initial value, we have a percent decrease, and our percent change is negative.

Our Percent Change Calculator below can help you solve for percent change, whether you're calculating percent increase or percent decrease, and can also help you find the initial or final values.

Percent Change in Voter Turnout

Percent increase and decrease tell us how things change, and in the real world, they are often used to determine the effects of certain policies. For example, voting is an important part of any democracy. Even if you can’t vote, the results of elections can affect how much medicine costs, how much you get paid, and even what classes your school teaches.

Because voting is so powerful sometimes, politicians who fear losing power create unfair policies and practices that prevent certain people from voting. This is often referred to as voter suppression. Using percent increase and decrease can help us determine the effects of voter suppression.

Let's look at this data from Michael McDonald, a political science professor at the University of Florida. We’ve rounded the numbers a little, but the table below shows the number of Black voters (in thousands) that voted early during the $2012$ and $2016$ presidential elections in four different states:

Which of these states had a decrease in early voter turnout between $2012$ and $2016$?

That’s exactly right! Of these four states, North Carolina was the only one whose early voter turnout decreased.

In $2013$, North Carolina passed a Voter ID law that required stricter voter ID, removed certain voting locations, and made early voting periods shorter. The law was struck down just before the $2016$ presidential election, but many suspected it would still affect voter turnout.

To see the effects of the Voter ID Law, let’s calculate the percent change for the number of early Black voters in North Carolina:

Amazing job! Our initial number was $754$, and our final was $688$. Now we just need to perform the calculations. Click the 🏆 when you’re ready to reveal the answer

The number of Black voters who voted during the early voting period in North Carolina decreased by $8.7\%$ between the $2012$ and $2016$ elections. According to the ACLU, in North Carolina, about $70\%$ of Black voters voted early in $2008$ and $2012$, so the $2013$ law would have had the largest effect on Black voters in the state.

Looking at the table, we can see that the number of Black voters who voted early increased in the other three states between $2012$ and $2016$. Since Florida, Louisiana, and Georgia did not change their early voting laws during this time, this data might lead us to believe that the $2013$ law led to voter suppression in North Carolina.