Interpreting the Similarity Score
Turnitin checks a user's work against its extensive database. If instances are found where a user's writing is similar to or matches against a source this will be flagged for your review in the match overview.
The database includes billions of web pages: both current and archived content from the Internet, a repository of works students have submitted to Turnitin in the past, and scholarly publications, which comprises thousands of periodicals, journals, and publications.
The color of the similarity score in 
My Files is based on the amount of matching text in a document.
What do the similarity score colors indicate?
The percentage range is 0% to 100% with the possible similarity groupings being:
A document's quotes and bibliography can be excluded from the similarity score.
Similarity scoring scenarios
A high similarity score does not always suggest that a piece of writing has been plagiarized, just as a low similarity score does not always indicate that no plagiarism has occurred. Consider the following scenarios:
Submitting a document of considerable size could result in a 0% similarity score with a report that still contains matches. This is because the similarity score has been rounded to 0%, rather than being exactly 0%.
You may have submitted multiple drafts of the same paper to your institution's private repository, meaning your final draft has resulted in a score of 100%. To avoid this issue, we advise that you only submit your final draft to the private repository.
An individual within your institution has managed to acquire a copy of your document. They submit this document to the institution's private repository and receive a similarity score of 25%. You submit your original document a week later to the private repository but receive a 100% similarity score.