I buy the actual CD. It has both the Windows and Mac versions on it. If you buy a download you need to buy the right one. They have both the Windows and Mac downloads. My friend buys the Mac download from Costco online.
Don't know when retail stores get their stock. They probably have the download online before the stores get the CD. Can't imagine that your credit union only has the Windows download. You might have to look for a checkbox to get the right version. Look close.
