There isn't a set percentage that is acceptable. Please note that Turnitin may sometimes also recognise your referencing as copied and pasted, however, if the referencing is done correctly you will not be marked down for it.
We would advise that if your similarity index is high and you want to reduce it, check that: (a) Quotation marks (“...”) are used around every quote and the source is cited, (b) you are not over-using quotations, and (c) your own words are not too similar to the original text.
Some Turnitin settings create a high similarity index that you can’t fix, for example when Turnitin matches quotations, bibliographies, and strings of commonly used text (5-8 words long).
If direct quotes are surrounded by double quotation marks (“...”) and the author is acknowledged, generally, Turnitin will ignore this text. However, some Harvard referencing styles use single quotation marks (‘...’). Turnitin recognises these as text matches rather than quotations.
Unfortunately, we do not support multiple submissions to Turnitin. You are welcome to use an online alternative to check the originality of your work. A popular one is Grammarly (please follow the link below):
Click here to go to the Grammarly Plagiarism Checker website
You can also sign up for Mendeley as a free alternative, using the link below:
Click here to get the Mendeley (free) Plagiarism Checker