There is no official minimum or maximum number of sources for an IB Extended Essay. For many essays, 10-20 carefully selected sources is a sensible working range, but this is practical guidance rather than an IB requirement. A Mathematics EE may need fewer, while a History or interdisciplinary essay may require more.
What matters is whether your evidence is credible, balanced and sufficient to answer the research question within the 4,000-word limit. From September to November, establish a strong core collection, begin drafting and add sources only when you identify a genuine gap.
The official IB position on source numbers
The IB Extended Essay overview describes the EE as an independent research paper of up to 4,000 words. The official Extended Essay subject brief requires references and a bibliography, but it does not prescribe a numerical target.
This reflects important differences between subjects. A literature essay might analyse one novel intensively, whereas a History essay may require archival evidence and several historians' interpretations. A science investigation may generate original data but still need scholarship to justify its theory and method.
The assessment model also depends on your examination session. Essays assessed from May 2027 use revised criteria outlined on the IB Extended Essay updates page. Neither assessment model awards marks simply for having a long bibliography, so confirm your session and current guide with your coordinator.
How many sources should you aim for?
Begin with 6-10 strong sources to test whether the question is researchable. As the argument develops, expand selectively toward approximately 10-20 sources if necessary. These are planning estimates, not official thresholds or grade boundaries.
The appropriate number depends on the subject, research method, availability of scholarship, complexity of the question and number of perspectives required. Original experiments, surveys or interviews may change the balance between primary evidence and secondary research, but they do not remove the need for academic context.
| EE area | Practical working range | Main priority |
|---|---|---|
| Language and literature | 1-3 primary texts plus 6-12 secondary sources | Keep close analysis central and use criticism to develop, not replace, your interpretation. |
| History and individuals and societies | 12-20 total sources | Combine relevant primary evidence with credible and contrasting scholarship. |
| Sciences | 8-15 secondary sources, plus relevant data | Support the theory, method, comparison and evaluation of findings. |
| Mathematics | 5-10 substantial sources may be sufficient | Prioritise mathematical reasoning and demonstrated understanding. |
| The arts | 8-15 sources, plus works analysed | Combine direct analysis with appropriate artistic and scholarly context. |
| Interdisciplinary EE | 12-20 sources is often reasonable | Ensure both subjects contribute through suitable concepts, methods and evidence. |
Read the official guidance for your chosen subject before applying any range. RevisionDojo's Extended Essay guide hub can clarify subject-specific planning, but your school's current IB documentation remains decisive.
Quality matters more than quantity
A useful source should perform a clear function. It might establish a theoretical framework, supply evidence, justify a method, introduce a competing interpretation or reveal a limitation in your argument.
Evaluate each source using four tests:
- Authority: Does the author or institution have relevant expertise?
- Evidence: Are the data, methods, reasoning or primary materials visible?
- Relevance: Does the source address the actual research question?
- Limitations: What bias, assumptions or restrictions affect its usefulness?
Peer-reviewed articles, academic books, official statistics and appropriate primary materials are usually stronger foundations than anonymous summaries. However, suitability depends on purpose. A newspaper may be weak evidence for a scientific claim but valuable primary material in a media or History investigation.
The RevisionDojo guide to choosing EE sources explains how journals, books, datasets and primary evidence serve different roles. Bibliography length matters far less than your ability to compare and analyse what you have read.
Organise sources by contribution
Citing the same article ten times does not create ten sources. One long book may provide several useful ideas, but it remains one scholarly perspective. A balanced collection normally includes foundation material, primary evidence, analytical scholarship, competing interpretations and method sources where appropriate.
Avoid allowing one author, institution or textbook to carry the entire essay. Comparing sources allows you to demonstrate synthesis and evaluation rather than presenting disconnected summaries.
A September-to-November source plan
Your school's internal deadlines take priority, but this schedule prevents open-ended research from delaying the draft.
| Period | Source goal | Main task |
|---|---|---|
| September | Find 6-10 credible core sources | Test feasibility, narrow the question and confirm the subject method. |
| October | Expand selectively toward 10-20 | Compare interpretations and build an argument-based outline. |
| November | Fill only specific gaps | Draft sections, test evidence coverage and audit citations. |
September: test feasibility
Do not collect 30 vaguely relevant links. Find a small core set and ask whether it provides evidence for more than one possible answer. If credible material is unavailable, revise the question early using the EE research question guide.
October: build a source matrix
Record each source's full citation, central claim, useful evidence, limitations and intended role. Add which sources it supports or contradicts. The EE research process guide offers further methods for organising evidence around claims instead of storing disconnected notes.
November: draft and fill gaps
Research should now become targeted. Draft a section, identify an unsupported claim or missing counterargument, and search specifically for that evidence. Use the EE time-management guide to balance this work with subject deadlines.
How to know when you have enough sources
You probably have enough when every major claim has evidence, expected source types are represented, key perspectives can be compared and credible alternative interpretations have been considered. You should also be able to evaluate important limitations rather than merely repeat information.
Another sign is source saturation. When credible searches mostly repeat evidence or interpretations you have already assessed, further collecting may contribute less than drafting and revision.
Citation rules still matter
Every borrowed quotation, paraphrase, dataset, image and non-obvious idea needs acknowledgement where it appears. The IB's Effective citing and referencing guide explains why listing a source only in the final bibliography is insufficient.
Use one consistent citation system approved by your school. Record page numbers and publication details while reading, then use RevisionDojo's IB citation checklist for a final audit. Never pad the bibliography with unread material.
Common source-count mistakes
- Chasing a numerical target instead of evaluating evidence
- Depending on general websites for major academic claims
- Saving sources without reading or understanding them
- Ignoring evidence that challenges the expected conclusion
- Treating primary research as a replacement for scholarship
- Leaving citations and page-number records until the end
Conclusion
The IB does not specify how many sources an Extended Essay needs. Begin with 6-10 core sources, expand toward roughly 10-20 when the argument requires it, and stop when the evidence is credible, balanced and sufficient. RevisionDojo's EE Guides, Jojo AI and Coursework Review can help identify unsupported claims and source gaps, although the final analysis and writing must remain your own.
Sources and referenced URLs
- IB Extended Essay overview
- IB Extended Essay subject brief
- IB Extended Essay curriculum updates
- IB Effective citing and referencing guide
- RevisionDojo Extended Essay guide hub
- RevisionDojo guide to EE research sources
- RevisionDojo EE research question guide
- RevisionDojo EE research process guide
- RevisionDojo EE time-management guide
- RevisionDojo IB citation checklist
