There is no acceptable similarity score percentage.
The similarity score is a measurement of how many of the words in the submission match words it can find online or in previous submissions. There are many factors that might affect the score. For instance, if you put the assignment wording or use a template, it will increase the score. Assignments that have you write pieces each unit and then submit the total at the end will have a very high similarity score because you already submitted portions of it. If your references are written correctly, they will likely be identified as copied because others have used the same references, as will any direct quotes. We even see a high similarity score when a lot of students use the same resource as a reference, such as the textbook or the first result in Google.
A high similarity score is a notice to you and your instructor that there may be a lot of matching text in the document. If you feel the score is higher than it should be, review the report. Thinking critically about why the report has matched text will help you determine if there is an issue or just a coincidence of copied text.
