"If" Clause

When the "if" clause at the end of the sentence is a modifier for a word in the main clause, there is no comma.
...I will go if I can scrape the money together.
...She will call if she gets there before 9:00.
When the "if" clause is not directly related to the content of the sentence -- which is often the case when it is reflecting a personal opinion -- there is a comma.
...He is going to go on for a higher degree, if you can believe that.
...She will send it to you tomorrow, if you so desire. Happy punctuating! Margie