What “substantial extension” usually means
Typical additions: fuller theory or proofs, new settings/tasks, systematic ablations, failure analysis, a longer related-work conversation. Promoting the appendix or swapping one dataset for the same claim is often thin.
There is no universal percentage; some journals colloquially want “a third or more new.” Make a private “conference vs journal” checklist before you write.
What to disclose at submission
In the cover letter or portal fields, name the prior conference title, venue, and year, and summarize what is new. Point to the conference version in a section or footnote so it does not look like hidden prior publication.
If figures reuse the conference paper, confirm the publisher’s policy—redraw when required. Explain author-list changes in one sentence.
- Disclose the prior conference version and the delta
- Check copyright and figure reuse
- Rewrite intro and related work for journal depth—do not paste the conference text
Timing and strategy
Some conferences constrain when journal extensions may appear; follow the proceedings copyright. While the conference paper is under review, do not dual-submit a near-identical journal draft.
If the new material could stand alone as another conference paper, that may be a better fit than a thin journal extension—depends on readers and evaluation timelines.
FAQ
- Must I cite my own conference paper?
- Yes. Hiding it looks like duplicate publication. Clear delta disclosure is safer than pretending the journal draft is brand new.
- Will the same reviewers see the extension?
- Not guaranteed. Write the new contribution so it stands without assuming memory of the conference version.