I really do not take this percentage too seriously. And I don't think you should.
You shouldn't write articles that are keyword spammed that's just the point of the whole thing. When you write naturally, you wouldn't have the time to start calculating how many percent does the keywords take up. Your article should sound natural while making sure the reader and of course Google is able to know what the page is talking about.
It's easier to get the reader to know/understand but with Google, you have to mention the keywords and related terms good enough times for it to pick up.
Every othet unnecessary calculation in my opinion is really unnecessary.
The method above has been working for me and still works till date.