((y2 - y1) / y1)*100 = your percentage change.

To calculate a percentage change, you can use this formula: (((y2- y1))/ y1) * 100. So, let's break this down with an example:

Suppose George owns stock in Vandelay Industries. His stock price went from $45 per share, to $47 per share. By what percentage has George's stock inceased ?

- We can set y1 = 45, and y2 = 47 (y1 is your first value, y2 is the value it changed to)
- Now subtract y2 - y1, which in our case is 47 - 45 which is 2
- Now divide 2 by 45 which is .044
- Multiply .04 * 100 which gives you 4.4

So George's stock has increased by 4.44 percent.