What is the optimal keyword density?

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.
The 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 optimised.

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

Keyword density, if that's what you're concerned about, has nothing to do with ranking and is pointless to worry about (unless you're stuffing the page with keywords, which isn't so good.

If you won't bother about it and just create your content than it will be ok. But 1-2% if enough if we are talking about exact numbers.

I like at least 1% and no more than 3%.

Just put in the keyword/s whenever you can put in relevantly, if you read your own post and start to sound like a robot no % is going to save you from Google's dick slappers

No more than 3%