Measure difference in an table

Good day all, 

I recently started building dashboards in Power-Bi and I'm now trying to start working with DAX formula's. 

In my dashboard I've created a table, with percentages per month. 

Now I would like to make the changes per period vissible. 

This is my table; 

How can I created an new colomn which calculates the difference between the last and previous period? 

Hope to hear from you guys.