How to Calculate Percent Change

Math doesn't come easy to all of us, and with the use of calculators and spreadsheets, it sometimes seems as though we'll never have to add, subtract, multiply or divide on our own again.
Occasionally, though, it may be necessary to calculate percent change--a company's income one year to the next, a budget increase from quarter to quarter, population growth over a 10-year period. Here is a simple way to do this math.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• pen/pencil and scrap paper
• calculator

1. Take the old value and subtract it from the new value, then divide by the old value.

2. Multiply by 100. That number represents the percent change.

3. Here's an example:
   
   Brayton School had 16 teachers in 1998. The next year, there were 12. What is the percent change from 1998 to 1999?
   
   Take 16 and subtract 12. That's 4. Then divide 4 by 16. That's .25. Now mulitply by 100 and you get 25. That's the percent change. The number of teachers at Brayton School went down 25 percent from 1998 to 1999.

[lixxi888]

on 1/21/2010 how do would you do this problem? "The regular price of a stereo is $250. With a 20% discount, what is the discount amount? What is the sale price?"

[philipmroberts]

on 1/1/2010 Short and easy to understand. Well written.

[bry4n]

on 12/6/2009 What you should do is NEW value minus OLD value divided by OLD value. THEN multiply by 100. Working it this way will also tell you if the percentage change took a negative shift or a positive shift. In this case it was a negative shift. It's easier for me to think of it this way. I just realized that Ricky above ^ said the same thing. Good observation Ricky. Hope this helps.

[crazyman2009]

on 8/4/2009 What if I have Brayton school (16 and 12 teachers), Crayton school (11 and 18) and drayton school (13 and 8) in my county and I want to calculate the % change in the number of teachers in my county? Is it ((12+18+8=38)-(16+11+13=40))*100/40 = -5% or [{(12-16)*100/12} + {(18-11)*100/11)} + {(8-13)*100/8)}]/3 = -10.73%

[csswenson]

on 6/19/2009 Alternatively, divide the recent period by the past period and subtract one, then multiply by 100: (RP/PP)-1*100. This equation is the same as above, just reformulated.