A number of times you should use your keyword in a guest blog

[FilkaCer]

Is it true that if you want to rank for a chosen keyword, you have to mention that keyword 3%-5% of the whole content (in a guest blog)?

[EGOL]

You should write in natural language.  That might produce a very different keyword density - especially if the article is really long.  Google can tell when you are stuffing in the keywords.  Readers think that you don't know how to write.

[jasongmcmahon]

The quality of the copy is more important than the number of times that the keyword is used, I aim for a 3% keyword density; regardless of the purpose of the copy.

[EGOL]

I absolutely agree that "the quality of the copy is more important than the number of times that the keyword is used."   I don't believe that I have ever calculated my keyword density because I believe that the quality of the copy is (almost) EVERYTHING.   Some people will scoff at this, but I know for a fact that if the quality of the copy is high enough that linkbuilding is not necessary... it enables you to spend all of your time on the copy.

[jasongmcmahon]

Whatever works for you, at times some calculation of keyword density may be required to avoid overuse.