Don't mind about keyword density, just make sure to include in your first and last sentence, in your h1-h2-h3 tags, and the rest will come naturally if your article is indeed focused around your keyword.

I learned this from Easy WP SEO sales page:

keyword density = (# of keyphrases / (total # of words / # of words in keyphrase))

Using this multi-word keyphrase formula, you’ll find that if the four-word keyphrase appears in 1,000 words of content 30 times, then

keyword density = (30 / (1000 / 4)) * 100 = 12%

Please, remember, keyword density is a vital factor whenever we talk about onpage SEO. So be sure of the following:
-At least the first 5 posts contain the main keyword. For example. If the site is: CHEAPLCDTVS.ORG the main keyword is: cheap lcd tvs
So the first 5 posts could be optimized for the following keywords:
cheap lcd tvs
cheap lcd tvs for sale
cheap lcd tvs online
cheap lcd tvs sale
cheap lcd tvs 32..
The keywords can be between 25-30% of the total text and the keyword repetition can be 2%-3%..

Just my 2 cents

As others have said, it's not that important, having your keyword on your page only once is often enough, and many times ive seen pages appear at the top of google and the page doesn't even have the keyword on it, just that the backlinks pointing at the site have used that keyword.

Now days keyword density doesn't really matter, just make sure that you wont repeat the keyword several times. Just right good and informative article and submit different places to build back links, cheers

Just make sure the keyword(s) you're trying to rank for are in the title, description and an H1 tag and you're good to go!

I wouldnt worry about the keyword density anymore as there are other more important things to do in SEO to gain good results. I would mx up the long tail a few times and then also spread the words throughout the article to give it a nice focus...however focus on the reader first and it will be naturally optimized...