There is no longer such thing as "keyword density". This should not be part of any SEO startegy.
Calculating this is a waste of time.
There are pages that rank without having the keyword on the page - seomoz has a good blog post on the subject by Rand I think.
It dose help to have the keyword on url and in the title tag and in h1 and at least once in the actual content but there is no magic formula.
I hate the statement "what is good for the user" as it is over used ny Google but in this case it dose make sense - it can be used once or 10 times or 100 times in the page as long as it make sense for the user and if you read the text is natural and no forced sentences or words. Synonyms of the word or alternative of the phrase are also a very good choice and google can associate those very well.
Personally I never take this in consideration to any of the projects - I used to (back in 2004-2005) when it was important but now based on industry opinions, google's statements and personal tests there is no magic formula and no help if you work on keyword density.
My 2 cents. Hope it helps.