Worked example
For 3,200 total words and 416 uniquely counted matched words:
416 ÷ 3,200 × 100 = 13%
“Unique” matters: if the same 20 words match three sources, they contribute 20 words—not 60—to the overall approximation.
A reproducible self-check method
- Fix the version: record filename, date, language and total word count.
- Define scope: decide in advance whether the title page, footnotes, appendices and bibliography are included.
- Name the comparison set: list sources and online services used. A personal source folder cannot reproduce Turnitin's databases.
- Mark matches: identify identical or highly similar word sequences and define a minimum length, such as eight consecutive words.
- Merge overlaps: combine overlapping spans and count each word position once.
- Calculate gross and adjusted values: one useful approach is to report all matches and a second value excluding correctly formatted quotations and the bibliography.
- Review every match: decide whether it is a correct quotation, valid paraphrase, common knowledge or a passage needing revision and attribution.
Why the actual Turnitin result can differ
- Depending on the school's setup, Turnitin compares internet content, publications and previously submitted work.
- The school can configure databases and exclusions for bibliography, quotations, cited text and small matches.
- An earlier submission of the same draft may match if it was stored in a repository.
- Other providers use different collections, preprocessing and match algorithms.
- The displayed score may change when an instructor excludes legitimate matches.
Describe a self-calculated value as an “approximation under the documented comparison procedure”, never as an exact predicted Turnitin score.