If i had a copy of my website in a subdomain, will that hurt my SEO?

[Ann]

A subdomain is as unique as another domain for crawlers. Both sites would be crawled and indexed, though the duplicate pages would not rank well on the keywords, as much as the main site should, given that you are taking care of ALL factors: on-site, on-page and off-page for your main site.

If you are really keen on having a subdomain, consider using it for content that is complementary to your main website. For example, the main domain could be your corporate website, but you could have a subdomain for each of your products / specialties. This would especially help if the main domain was a proper noun (without a dictionary definition), but the products/services added as subdomain would give that much keyword impact to your ranking strategy.