IB Computer Science: The Complete Guide (2025-2027)

By Michael Thompson · Former IB Diploma Programme coordinator; 10 years at Bromsgrove School · Published 4 September 2026

IB Computer Science is a Group 4 science subject in the IB Diploma Programme, available at Standard Level and Higher Level, with first teaching of the updated syllabus beginning August/September 2025 and first assessment in May 2027. The course blends theoretical computer science - computational thinking, algorithms, networks, databases, and machine learning - with a substantial practical component in the form of a coded internal assessment. Choosing between HL and SL matters: HL adds extra topics, an additional exam paper, and around 60 more guided hours. This guide covers the full syllabus structure, the internal assessment requirements, the case study paper, programming language expectations, and how universities view the subject - so you can make informed decisions about how to study it.

Key Takeaways

In This Article

  1. What Is IB Computer Science and Who Is It For?
  2. The 2027 Syllabus: Core Topics at a Glance
  3. HL vs SL: How Higher Level Computer Science Differs
  4. Assessment Model: Papers, Weightings, and the Internal Assessment
  5. The IB CS Internal Assessment: Building a Computational Solution
  6. The Case Study Paper: What It Is and How to Prepare
  7. Programming Languages and Pseudocode Conventions
  8. Key Algorithms and Data Structures You Need to Know
  9. How Universities View IB Computer Science
  10. What to Do Next

1. What Is IB Computer Science and Who Is It For?

IB Computer Science is a Group 4 subject in the IB Diploma Programme, available at Standard Level (SL) and Higher Level (HL). The updated course has first teaching from August/September 2025, with first assessment in May 2027. If you are starting the Diploma in autumn 2025, this revised syllabus is the one you will sit.

The subject suits students heading toward computer science degrees, software engineering, data science, or any field with a quantitative and computational foundation. It also works as a rigorous science option for students who want something beyond biology or chemistry, though one important detail catches people out: universities classify IB CS differently. Because computer science sits within the DP sciences subject group, some admissions teams count it as a science for entry purposes, while others treat it as a technology subject and require a traditional lab science alongside it. That distinction matters if your target course specifies "a science subject" in its conditions, so checking university-specific entry requirements early is worth doing before you finalise your subject choices.

The course is one of the six subjects every Diploma student selects, taken alongside the core elements of Theory of Knowledge, the Extended Essay, and Creativity, Activity, Service (CAS). You choose whether to study it at SL or as one of your three to four HL subjects, and that choice shapes both workload and the range of universities that will find the qualification useful.

2. The 2027 Syllabus: Core Topics at a Glance

The updated IB Computer Science course begins first teaching in August/September 2025, with first assessment in May 2027. The full subject guide is available via ibo.org. The IB describes its curriculum reviews as a collaborative process aimed at producing "internationally-minded, research-based curricula", incorporating the latest educational research and lessons from evaluating the existing course.

The syllabus is built around six core strands, all of which are shared by both SL and HL students before any HL-specific extensions apply:

StrandWhat it covers
Computational thinking and problem-solvingAbstraction, decomposition, algorithmic design, and problem analysis
ProgrammingCode logic, object-oriented concepts, and the IB's own pseudocode conventions
Data structures and algorithmsArrays, linked lists, stacks, queues, trees, sorting, and searching
NetworksProtocols, architecture, and data transmission
DatabasesRelational models, SQL fundamentals, and data integrity
Machine learning and AISupervised and unsupervised learning, model evaluation, and ethical considerations

One non-obvious point: the machine learning strand is genuinely new to this version of the course and is shared across SL and HL. That means SL students are expected to engage with neural network concepts that previously appeared only in HL extension material or not at all. It is not a simplified overview appended to the end of the course. Plan your time accordingly.

Section 3 covers what HL adds on top of this common core.

3. HL vs SL: How Higher Level Computer Science Differs

!IB Computer Science HL vs SL comparison showing papers, hours, and extra HL topics.webp7860

Per the IB's own structure, every Diploma Programme student takes at least three and no more than four subjects at Higher Level, with the rest at Standard Level. Computer Science can sit in either tier, and the choice has real consequences for your workload and your university options.

What HL adds over SL:

The non-obvious trade-off: SL Computer Science is not an easy ride. The internal assessment, the pseudocode conventions, and the algorithmic thinking are identical at both levels. What changes is the ceiling, not the floor. Students who pick SL expecting less rigour than SL Mathematics, for example, are sometimes caught out by the programming demands.

When to pick HL:

On that last point: IB course selection guidance notes that universities categorise subjects as "required," "preferred," or "recommended." Those are meaningfully different thresholds, and you should check each target university's entry requirements individually rather than assuming HL is always necessary or always sufficient.

4. Assessment Model: Papers, Weightings, and the Internal Assessment

The assessment structure differs between levels in one important way: HL students sit three external papers, SL students sit two.

SL assessment:

HL assessment:

The IA contributes a significant portion of the final grade at both levels. This matters more than many students expect, because the IA mark is entirely within your control before the exam season begins, unlike the time-pressured paper questions.

One non-obvious point: Paper 3 at HL is not a generic extension of the core content. It tests a specific pre-released case study, so preparation for it is fundamentally different from revision for Papers 1 and 2. Treating it as an afterthought is a common mistake among HL candidates.

Important caveat on exact weightings. The 2027 syllabus subject brief had not been publicly released at time of writing. Percentage weightings for each component can shift between curriculum cycles. Always verify the current breakdown directly against the published DP subject brief, which the IB makes available at ibo.org/university-admission/latest-curriculum-updates. Never rely on third-party summaries for official figures.

5. The IB CS Internal Assessment: Building a Computational Solution

!IB Computer Science internal assessment five-stage process flow from problem identification to evaluation.webp11688

The IB CS internal assessment is a student-developed computational product: a working program or system built to solve a real problem for a real, named client or end-user. This is not a report about software or a theoretical proposal. The examiner expects functional code, evidence of a design process, and documentation that shows how your thinking developed from the client's problem to the finished product.

What the documentation requires

You will produce a structured set of written records alongside the product itself:

Assessment criteria

The IB assesses the IA across categories broadly covering Planning, Design, Development, Functionality and Extensibility, and Evaluation. **Check the exact criterion labels, descriptors, and weightings in the official subject guide at ibo.org**, particularly given that the updated course has first teaching from August 2025, with first assessment in May 2027.

The non-obvious pitfall

Scope is where most IAs go wrong. A small, well-documented system with clear evidence of computational thinking will outscore an ambitious project with thin planning records and unexplained code. Examiners cannot award marks they cannot see in the documentation. If a design decision is not written down, it does not exist for assessment purposes. Choose a client with a genuine, bounded problem, agree specific measurable success criteria at the start, and document every significant decision as you build.

6. The Case Study Paper: What It Is and How to Prepare

The case study is a pre-released document published by the IB several months before the May examination session. It is the sole basis for Paper 3, which is an HL-only paper. SL students do not sit Paper 3 at all, so the case study is one of the clearest practical distinctions between HL and SL subjects in this course.

The document describes a real-world or realistic technological scenario, a business system, an emerging technology, a social platform, or similar. Exam questions are then set entirely within that scenario's context, asking you to apply computer science concepts to the specific situation described, not to generic textbook examples. That framing matters: an answer that ignores the scenario and gives only abstract theory will lose marks even if the technical content is correct.

How to prepare, step by step:

  1. Read the case study in full at least three times before you begin researching anything. Annotate unfamiliar terms on your first pass.
  2. Extract every technical concept it references, explicitly or implicitly, and build a topic list. A case study about a distributed payment system, for example, implies you need to know networking protocols, data integrity, and encryption.
  3. Research each concept independently using textbooks, the IB subject guide, and revision resources. The goal is depth on a narrow set of topics, not broad coverage.
  4. Practise writing exam-style responses that name specific details from the case study document, not generic examples.
  5. Review past case studies from the pre-2027 syllabus. The content will differ, but the question style and the expectation that you link theory tightly to the scenario stays consistent.

One non-obvious gotcha: the IB deliberately omits some technical detail from the case study itself, expecting you to research beyond the document. Students who only annotate what is written, without investigating what the scenario implies, often find themselves unable to answer the higher-mark questions.

7. Programming Languages and Pseudocode Conventions

IB Computer Science does not mandate a single teaching language. Schools choose whatever suits their context, and Java and Python are the most common picks, though some use C++, JavaScript, or another language entirely. The same freedom applies to the Internal Assessment: your solution can be written in any language your school supports.

The catch arrives in the written exam papers. The IB uses a standardised pseudocode notation across all papers so that every student, regardless of what language they learned in class, reads and writes algorithms in the same format. This notation has its own specific keywords, loop structures, and conventions that do not map exactly onto Python or Java syntax. One non-obvious quirk: the IB pseudocode uses `output` rather than `print`, and its collection-access syntax differs enough from Python that students who never practise it often misread loop boundaries under exam pressure.

The IB publishes an approved notation reference, sometimes called the pseudocode booklet or notation sheet. Obtain a copy from your teacher or the IB's official resources early in the course, not the week before exams.

Practical tip: take any algorithm you have written in your school's language and rewrite it in IB pseudocode regularly. The translation process is where the gaps show up. Students who only code in Python and never practise the notation tend to lose marks on Paper 1 algorithm questions not because they cannot solve the problem, but because their notation is ambiguous or incorrect.

8. Key Algorithms and Data Structures You Need to Know

Algorithm questions appear across all three written papers, so your ability to trace, write, and analyse them in IB pseudocode (not Python, not Java) is what the mark scheme tests. Many students learn to code these in their preferred language but then stall on exam questions because the IB notation has its own conventions for loops, array indexing, and output statements. Practise writing the pseudocode form specifically.

The algorithm categories you need to cover:

Core data structures:

For practice questions filtered by paper, level, and topic, the official source is the IB Questionbank, created by the IB and available through the Follett IB Store (Titlewave). It lets you pull past DP Computer Science questions by examination date, paper, or question type, which makes targeted algorithm revision straightforward. A time-limited demo account is available before you commit to a licence.

9. How Universities View IB Computer Science

IB Computer Science sits in Group 4 (Sciences), but that classification does not automatically satisfy a science requirement at every university. Per the IB's own course selection guidance, universities apply three distinct categories when assessing subjects:

Where HL CS falls in those categories varies by institution and by programme. A university might accept HL CS as satisfying a science condition for a Computer Science degree, while the same university's Engineering faculty requires Physics HL instead. The group placement does not decide this - the admissions team does.

A concrete example of how this plays out internationally: IU International University of Applied Sciences in Germany specifies one science (Biology, Physics, or Chemistry) separately from the 6th subject slot, where IB Computer Science is listed as an eligible option. In other words, CS there fills a breadth slot, not the science requirement.

For UK students considering IB Computer Science, requirements across UK universities vary significantly enough that checking each institution's entry requirement pages directly is the only reliable approach. Do not assume a Russell Group offer letter's wording mirrors another university's conditions, even for courses with identical names.

10. What to Do Next

If you have not yet chosen between SL and HL, do this first: download the official IB Computer Science subject brief from ibo.org, which sets out the full assessment model for the 2027 first-examination cohort. The brief shows the exact paper weightings and IA requirements at both levels in one place, so you can compare them directly before committing.

If you are already enrolled on the 2025 first-teaching course, track the IB's annual case study release date. Most students do not start annotating it until the spring term, which is too late. Reading and annotating it the week it drops is the single step that separates confident HL Paper 3 candidates from those scrambling to catch up.

Check the subject brief this week. Then note the case study release in your calendar now.

FAQ

Is IB Computer Science hard?

Difficulty depends on your background, but the combination of theoretical exam papers (including algorithm tracing in IB pseudocode), the substantial internal assessment, and - for HL - a pre-released case study paper makes it one of the more demanding Group 4 options.

What programming language is used in IB Computer Science?

The IB does not mandate a specific language; schools typically teach Java or Python, but exam papers use the IB's own approved pseudocode notation so all students answer algorithm questions consistently.

How long is the IB Computer Science internal assessment?

The IA is a computational product - a working program - accompanied by detailed planning, design, development, and evaluation documentation; word or page limits are set in the official subject guide available on ibo.org.

What is the IB Computer Science case study?

The case study is a document pre-released by the IB before the May exam session; HL students study it in advance and are examined on it in Paper 3, which sets questions within the scenario described in the case study.

Does IB Computer Science count as a science for university entry?

Computer Science sits in Group 4 (Sciences), but whether a university counts it toward a science-specific entry requirement varies - students must check each university's own admissions pages.

What is the difference between IB Computer Science HL and SL?

HL covers additional content beyond the SL core, sits an extra paper (Paper 3, the case study paper), and requires more guided learning hours; SL students take Paper 1 and Paper 2 plus the internal assessment.

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