Breaking down city, state, and zip from one column into 3

I am working in Excel, and have City, State, and Zip code in one column. I wish to break down the column into 3 separate columns: Col. 1: City, Col. 2: State, and Col. 3: Zip.
I know how to do that, and I'm using the LEN formula to extract what I need from the first column. However, I have ran into a problem. In the zip code column, I have some 5 digit zip codes while others are 9 digits. Once I use the len formula, it extracts the state as well as the zip code for all the 5 digit zips. Is there something else I can do to only extract the zip codes whether they are 9 or 5 digits? Please help! Thanks!