Formula to show percent increase/decrease

I am trying to add a formula in Excel to show a percent increase or decrease in sales from one month to the next and I can't figure out the formula...Columns are: month and total sales(in dollars). I need to compare month 2 to month 1 and show how much the sales increase or decreased on a percentage basis (Ex: January $10,000 and February $15,000...the answer I want is a positive 50%.)

Thanks.

Re: Formula to show percent increase/decrease

Thanks for the fast help. I think my middle school math teacher is going to hunt me down now for being so dense.

A.