Self-plagiarism isn't a myth or an AI-detection side effect — university library guides treat it as its own, distinct academic-integrity category: submitting your own previous work, in whole or substantial part, for a new assignment without your instructor's permission. Whether Turnitin specifically catches it depends on a mechanism that's less universal than people assume: a submitted-paper repository whose scope is set by each institution, not one fixed global rule.
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University library guides — from institutions like the University of Arizona, the University of North Texas, and Duke's Text Recycling Research Project — describe self-plagiarism (sometimes called "text recycling") as submitting your own previously written work, or a substantial part of it, for a new assignment without your instructor's permission or without citing the earlier version. It's treated as a distinct issue from plagiarizing someone else's material, but it still commonly falls under a school's academic-integrity policy, since the concern is representing old work as new, original output for a second assignment.
The practical implication: "it's my own writing" isn't automatically a defense. Whether reusing (or substantially overlapping with) your own past paper is allowed for a given assignment is a policy question your specific course or institution answers — some explicitly permit building on your own prior work with disclosure, others don't.
Turnitin generates its similarity report by comparing a submitted paper against several sources: current and archived web pages, academic publications, and a repository of previously submitted files. That last category is the one that matters for self-plagiarism — if your own earlier paper is stored in the repository your instructor's Turnitin account draws from, a new submission that substantially overlaps with it can surface as a similarity match, the same way it would against any other stored source.
The part that's genuinely institution-specific: whether — and how broadly — that repository stores and shares submitted work varies by school. Some universities' Turnitin setups keep submissions private to that institution and don't feed them into a shared cross-institution pool; others opt into broader repository participation. That means whether a paper you submitted last semester is even in the comparison pool for a different class depends on your specific institution's configuration, not a single rule that applies everywhere.
StudyPilot's plagiarism checker compares your draft against web pages, academic papers, and a broad student-submission database — the same general category of source Turnitin also checks against. What it can't do is see inside your specific institution's private Turnitin repository, so running an old paper through it won't reliably tell you whether your school's Turnitin setup would flag it as matching your own earlier submission.
What it's genuinely useful for here is the more common case: catching unintentional overlap with outside sources in a draft you believe is original, before you submit it. If the actual question is whether reusing your own past work is allowed for a specific assignment, that's worth asking your instructor directly rather than treating any plagiarism checker's result as the answer.
StudyPilot's plagiarism checker scans your paper against web pages, academic papers, and student submissions — a useful pre-check, even though it can't see your school's own private Turnitin repository.
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