IB Biology SL 2025 Grade Boundaries Guide (Marks You Really Need)
If you are sitting IB Biology SL in May 2025, you are probably wondering one thing: “How many marks do I actually need for a 6 or 7?”
Grade boundaries feel scary, but they are just numbers that decide where each grade starts and ends. Once you see them clearly, they stop being a mystery and start becoming a plan.
In this guide, you will see the IB Biology SL 2025 grade boundaries for the May session, both overall and by paper. You will see how many marks you need for each grade from 1 to 7, and how that links to your study goals. Everything is broken into simple, clear steps so you, your parents, or your teacher can follow it.
For extra context or to double-check the ranges, you can also look at the official IB Diploma statistical bulletin page.
What Are IB Biology SL Grade Boundaries in 2025 and Why Do They Matter?
Grade boundaries are the minimum marks you need for each grade. For IB Biology SL, your final mark out of 100 is split into bands. Each band is a grade from 1 to 7.
For example, if the boundary for a 7 starts at 76, then a total of 76 out of 100 gives you a 7. A total of 75 puts you at a 6. That single mark can change your final result.
Boundaries can change each exam session. If the exam is harder, the IB lowers the marks needed for each grade. If it is easier, the marks may go up. In this article, all the numbers are for May 2025 IB Biology SL.
These boundaries matter a lot for:
- Predicted grades your teachers send to universities
- Entry to courses like medicine, biology, and engineering
- Meeting school or scholarship requirements
The main difference between a 5, 6, and 7 is often only a handful of marks, which is why understanding the boundaries is so helpful.
How the IB 1 to 7 scale works for Biology SL
Here is a simple way to think about the 1 to 7 scale:
- 7: Excellent understanding, strong exam skills
- 6: Very good, only a few weak spots
- 5: Good, but some gaps in knowledge or exam technique
- 4: Satisfactory, basic understanding, some missing pieces
- 3: Limited, struggles with many topics
- 2: Very limited, major gaps
- 1: Very poor, almost no correct understanding shown
Most schools see a 4 as the minimum pass. Many students who want science or medicine aim for at least a 6, and often a 7.
Why grade boundaries change from year to year
IB does not want one year to be “harder” or “easier” than another in terms of grades. So it adjusts grade boundaries after it sees how students did.
Think of it like this:
- If Paper 2 is much harder than expected, then the mark for a 7 might be a bit lower than last year.
- If Paper 1 is quite easy, you might need a slightly higher mark to get the same grade.
This keeps the final grades fair across years. For this guide, all the numbers come from May 2025 Biology SL boundaries, not guesses or predictions.
IB Biology SL May 2025 Grade Boundaries Explained (Marks for Each Grade)
Let us start with the big picture, your overall mark out of 100.
Overall IB Biology SL 2025 grade boundaries (out of 100)
For May 2025, the official overall boundaries for IB Biology SL are:
| Grade | Total marks out of 100 |
|---|---|
| 7 | 76–100 |
| 6 | 64–75 |
| 5 | 52–63 |
| 4 | 40–51 |
| 3 | 26–39 |
| 2 | 14–25 |
| 1 | 0–13 |
Your final grade comes from your exam papers plus your internal assessment (IA or practical work), all combined into this total out of 100.
Notice how tight the bands are near the top:
- The gap between a 6 and a 7 is only 1 to 12 marks.
- The gap between a 5 and a 6 is only 1 to 12 marks as well.
This means a small improvement in each paper, maybe just a few marks, can push you into the next grade band.
Paper 1, Paper 2, Paper 3, and practical work grade boundaries in 2025
IB Biology SL has three exam papers plus your practical work:
- Paper 1: multiple choice, out of 30 marks
- Paper 2: short answer and longer response, out of 50 marks in the boundaries table
- Paper 3: data based and option questions, out of 35 marks in the boundaries table
- Practical work / IA: your investigation and lab work, often marked out of 24 at school level
Here are the May 2025 boundaries for the written papers:
| Component | Out of | Grade 7 | Grade 6 | Grade 5 | Grade 4 |
|---|---|---|---|---|---|
| Paper 1 (MCQ) | 30 | 24–30 | 20–23 | 17–19 | 13–16 |
| Paper 2 | 50 | 39–50 | 33–38 | 26–32 | 20–25 |
| Paper 3 | 35 | 25–35 | 21–24 | 18–20 | 14–17 |
For practical work / IA, many May 2025 summaries describe the bands roughly as:
- Grade 7: 20–24
- Grade 6: 17–19
- Grade 5: 14–16
These IA marks are then scaled and added into your total out of 100.
Each part of the course counts. Weakness in one paper can be balanced by strength in another, but missing a whole component, like not submitting the IA, can drag your total down a lot.
How your final IB Biology SL grade is calculated from all parts
Your teacher or the IB converts each component to a scaled mark. These are combined to give a single score out of 100, then the table above turns that total into a 1 to 7 grade.
Here is a simple example student:
- Paper 1: 21 out of 30
- Paper 2: 36 out of 50
- Paper 3: 23 out of 35
- IA: scaled so the final combined total is 77 out of 100
A total of 77 sits in the 76–100 band, so this student gets a 7 in IB Biology SL. A few marks lower could have dropped them into the 6 range, which shows how important each mark can be.
How Many Marks Do You Need in IB Biology SL 2025 for Your Target Grade?
Once you know your target grade, you can turn it into a clear mark goal.
Aiming for a 7 in IB Biology SL 2025 (top grade strategy)
For a 7, you need at least 76 out of 100. That is about three quarters of all the marks.
To stay safe, aim a bit higher than 76 in practice, since you might have a bad day on one paper. A simple way to think about it:
- Try to score around 80% on past papers.
- Aim for a strong IA, as close to the 7 band as you can.
Focus on:
- Deep understanding of the core content, not just memorizing notes
- Lots of practice with data based questions and long answers
- Careful review of past paper questions and mark schemes
Targeting a 6 or 5 (strong and solid passes)
A 6 is 64–75, and a 5 is 52–63.
A typical 6 student:
- Understands most topics well
- Loses marks on tricky data questions or time management
- Might have one weaker paper but solid results on the others
A typical 5 student:
- Has a decent base, but some topics are shaky
- May leave parts of questions blank or answer too briefly
Simple goals:
- For a 5, try to score a bit above half marks on each part.
- For a 6, aim for around two thirds of the marks on each part.
To move from a 5 to a 6, or a 6 to a 7:
- Fix common mistakes using mark schemes
- Practice writing to the command terms
- Clean up your IA structure and analysis
Reaching at least a 4 in IB Biology SL (secure pass planning)
A 4 is 40–51. Many schools and programs see this as the minimum passing grade for the subject.
If you feel behind, a 4 is still very possible with a clear plan. Aim to reach a little above 40 marks total. Do not skip any part of the course.
Key advice:
- Attempt every question, even if you are unsure
- Complete your IA fully and meet all deadlines
- Learn the most tested topics well, like cell biology, genetics, and ecology
- Practice short answers to pick up “easy” marks
Small wins, such as gaining 1 or 2 extra marks on each paper, can be enough to pull you from a 3 to a 4.
Smart Study Tips to Move Up a Grade Boundary in IB Biology SL 2025
Grade boundaries are not just numbers. They can guide your study plan.
Use past papers and mark schemes to train for the 2025 boundaries
Past papers are your best way to check if you are in the 4, 5, 6, or 7 range.
Try this routine:
- Do a full paper under timed conditions.
- Mark it with the official mark scheme.
- Compare your score with the May 2025 boundaries for that paper.
- Track your total out of 100 and see which band you sit in.
Focus on why an answer is right or wrong. Copying the mark scheme wording teaches you what examiners want to see.
Focus on command terms and data based questions
Many students lose marks because they do not follow the command terms:
- Describe: say what you see
- Explain: give reasons and links
- Outline: give a brief summary
- Evaluate: give pros, cons, and a reasoned judgment
Short daily practice with command terms can raise your Paper 2 and 3 scores. Combine this with regular work on:
- Graphs
- Tables
- Experimental setups and errors
These skills matter a lot for students who sit near the line between a 5 and 6, or a 6 and 7.
Do not ignore your practical work and IA marks
Your IA and practical work can give you a big boost. A strong IA in the 20–24 range (grade 7 band) can help lift a weaker exam score into a higher overall grade.
To get the most from your IA:
- Start early and give time for teacher feedback
- Keep your graphs clear and labeled
- Link your results to Biology theory, not just to the numbers
- Check that you have met all the IB criteria
Improving your IA by even 3 or 4 marks can be one of the easiest ways to jump a whole grade boundary.
Conclusion
For May 2025 IB Biology SL, the key facts are simple: a 7 starts at 76, a 6 at 64, a 5 at 52, and a 4 at 40 out of 100. Your three papers and your IA all combine to give this final total, and the difference between grades is often only a few marks.
Use these grade boundaries as a guide, not as a source of stress. Turn them into practice targets, track your scores, and aim for small gains in every paper and in your IA. With steady work and smart planning, moving up a full grade band is realistic, even if it feels far away right now.