Is there SEO penalties for having .htm homepage?

[Kurtyj]

In the past, I have had very good SEO rankings but have recently slipped.  I am trying everything I can.  Only my home page has domain/index.htm while all other pages have .html suffixes.  I have been reluctant to change the home page worrying that it could further hurt my SEO.

QUESTION

Does it even matter?  If so, will changing home page to .html have any adverse effects for SEO?

[My-Favourite-Holiday-Cottages]

Changeing any url to any other url without a proper 301 on the old url can have adverse effects, as old links then go to 404 pages. I wouldn't expect however there to be a gain or loss for that inconsistancy in your url structure, save in people linking to .html by mistake.

Also as a slightly less SEO related note, for best ux, try getting rid of the .filetypes entirely, and in the homepages case rid of the index too. This mostly helps with the homepage, reducing the odds of needing a 301 for the link to reach you correctly.

[KevinBudzynski]

IMHO, page extensions doesn't matter for ranking (the spiders are more concerned on what is on the page). However, there are positive aspects on being consistent.

Changing the page to .html and having the proper redirect will most likely yield no change. However, there is discussion on a dampening effect, but I don't think anyone really knows (except G's engineers). Great article on it.

[EGOL]

Don't change a URL just because it is htm instead of html.

That change will have ZERO positive impact.  ZERO.