How to choose IB subjects: the group rules, HL vs SL, and what universities need

To choose IB subjects, pick one subject from each of groups 1 to 5, then either an arts subject or a second subject from another group, and take three or four of the six at Higher Level (HL). Make the choice in this order: first check what the university courses you might apply for require, then choose HLs you are both good at and willing to spend extra time on, then check the combination is a workload you can actually carry for two years.

What are the rules for choosing IB subjects?

• Six subjects: one each from groups 1–5, plus group 6 or a second subject from groups 1–4.
• Three or four at HL, the rest at Standard Level (SL).
• ESS is interdisciplinary: it can count as group 3, group 4, or both. Counting it as both frees a slot for another subject from any group.
• Two group 1 subjects instead of a group 2 subject is possible for students with two strong languages, and is one route to the bilingual Diploma.

Your school's own list limits all of this. Most schools timetable subjects in blocks, so two subjects you want may clash. Ask for the block plan before you fall in love with a combination.

What is the difference between HL and SL?

HL subjects have 240 recommended teaching hours; SL subjects have 150. That is 90 extra hours per HL subject, and in most subjects it shows up as extra content and a longer or extra exam paper. HL and SL grades carry the same points.

What HL actually adds in the subjects Heptavo covers:

Two patterns are worth knowing. First, in the sciences, HL contains all the SL content plus more, so moving from HL down to SL mid-course is usually easier than moving up. Second, the IA weight is often the same at both levels (20% in Biology, Chemistry and Maths), so at HL your exam performance carries the extra content.

Which HL subjects do universities want?

This is the question to answer first, because it is the one with hard constraints. Some courses name specific HL subjects and grades; if you do not take them, you cannot meet the offer.

Patterns you will often see, but must check course by course:

• Medicine, dentistry, veterinary science: commonly HL Chemistry, often with HL Biology. Some courses accept either science at HL if the other is at SL; others do not.
• Engineering, physics, computer science: often HL Maths (frequently specifying AA) and sometimes HL Physics.
• Economics and other quantitative social sciences: may specify the maths course or level.

How to check properly:

1. List three to five courses you might apply for, in the countries you are considering.
2. For each, open the IB entry requirements on the university's own course page.
3. Write down every named subject, level, grade and maths course (AA or AI).
4. Choose your HLs to cover the strictest of these.

Do this early. UK applicants for medicine, Oxford and Cambridge face a mid-October deadline at the start of DP year 2, so your subjects and predicted grades matter long before your exams.

Should you take Maths AA or AI?

Both exist at SL and HL. The biggest practical difference is the calculator: AA Paper 1 is calculator-free, while every AI paper allows a graphic display calculator. AA leans towards algebra, calculus and proof; AI leans towards modelling, statistics and technology. Some university courses specify AA, sometimes at HL, so check your list before choosing. Our Maths AA vs AI comparison goes through the papers in detail.

How do you balance the workload?

Hours are the honest measure. Three HLs plus three SLs is about 1,170 recommended teaching hours (3 × 240 + 3 × 150); a fourth HL replaces 150 hours with 240. On top of that come TOK, the Extended Essay (about 40 hours of your own time) and CAS.

Some checks before you commit:

• Count the exam hours. HL Biology, HL Chemistry and HL Maths AA add up to 14 h 15 of HL exams alone, compared with 3 hours for each SL subject.
• Count the coursework. Nearly every subject has an internal assessment, so six subjects usually means six IAs, plus the EE and the TOK essay and exhibition. Two IAs that both need lab or field data in the same term is a real squeeze.
• Use the grade rules. You need at least 12 points from your HLs. An HL you are likely to score 3 in is a genuine risk to the Diploma, whatever your SL grades. See how IB scoring works for the full set of conditions.
• Think about the EE now. We suggest writing the Extended Essay in a subject you study and enjoy, so your HL choices shape your EE options. See choosing your EE subject.
• Try the level. Ask current DP2 students about their weekly workload, and look at a few HL-level questions in each candidate subject before choosing.

Choosing a subject because your friends take it, or because one teacher is popular, is a weak reason for a two-year commitment. Choosing it because you would happily read about it in your free time is a strong one: that interest is what gets you through the IA.

Can you change IB subjects later?

Usually, within limits that your school sets. Common patterns:

• Early in DP year 1 is the easiest time to change, before much content and coursework has built up.
• Dropping from HL to SL is generally simpler than the reverse, because HL includes the SL content. Moving up means catching up on HL-only material.
• Switching subject entirely later in the course means catching up on content and possibly an IA, and may be impossible if the timetable is full.
• Changing your maths course (AA to AI or the reverse) is possible at many schools early on; ask.

Before changing, check two things: whether any university course on your list needs the subject you are dropping, and whether your EE is in that subject. Your DP coordinator registers you for exams with the IB and knows your school's deadline for changes. The IB timeline shows where that falls in the two years.