What is the optimal keyword density?

[Mike T]

I am using Yoast SEO plugin which comes very highly recommended. It suggests that keyword density should not be more than 2,5%. Harsh Agrawal from Shout me load recommends approx 1.5% and if you google the question his article is 1st or 2nd place.
Also, I have come across quite a number of articles suggesting that keyword density is not really an important metric for ranking in the SERPs. I surely hope I have not wasted all the effort of ensuring my posts are all keyword optimized.

So to boil down to the bedrock of my question - What is the optimal keyword density?

[webxerossolutions]

Keyword Density is the percentage of the number of times a keyword appears on a web page. In recent days, keywords matter much less than site quality, but it doesn't mean that keyword density holds no value in SEO. Some people have a myth, if we use our keyword many times it will rank higher in the search engine.  But in actual, Google considers it as a keyword spamming. 
There is no exact percentage for better ranking. According to me, 1.2% of keyword density is better along with LSI keywords.