As with many of the other density topics on here, it is important not to focus too closely on density, but to write relevant content that will appeal to your readers.
This is for Yahoo. Coming to Google, if you use 3 - 8% you will be penalized by Google. You can use keyword density of 3-5% for all search engines. Best usage is 3.5-4%.
No such thing as keyword density. Google is looking for content that is relevant and natural, there is no "if you mention it as more than 8% of total text we will ban you" bit in their algorithm. Most SEO's of merit seem to say nowadays that you only need to mention your key term around once every 100 words. Google has got a lot better at spotting natural text that is on topic through its associative words and terms capability, so you really do not need to worry about keyword density. Just write naturally and make sure its on topic - Google will associate it with the keyterms anyway.
I suggest 3% as optimum. But keep your content good and quality. Create your webpage for users and not for keywords.
Hello, Do not worry about keyword density, analize your competitors, for example if you want to rank "red cards", take a look the first 10 possitions in Google/Yahoo or bing, and then check out the keyword density, work on every keyword that you want to rank, in many cases the keyword density is 20% and in another one has 1%. My 2 cents, Jakomo
Sometimes I think people can think too much about SEO. If you simply write a natural page about a single topic or closely related group of topics, Google is going to know what the page is about. The solution is to not worry about density and just write the content as if you really wanted people to like it
I'll suggest it 2% to 7% for your major keywords. your content should be natural then if density doesn't matter. Nowadays more people check the LSI.