Grade Boundaries Explained
A student-friendly guide to how thresholds work across Cambridge, Edexcel and the IB — and how to use them
What you'll learn
- What a grade boundary (threshold) actually is
- Why the mark for each grade changes every session
- How Cambridge, Edexcel and the IB each set and publish them
- How to turn your raw mark into a grade — and where to find the official numbers
What is a Grade Boundary?
After every exam session, the board publishes a table showing the minimum mark needed for each grade on each paper. Score on or above the boundary and you get that grade.
Illustration only — a made-up sample paper (marked out of 80)
These are round numbers to show the idea. They are not real boundaries for any actual paper.
68/80
60/80
50/80
40/80
32/80
In this made-up example, 60 or more would be an A, and 68 or more an A*. Every real paper and session has its own boundaries.
Why Do Boundaries Change?
There is no fixed percentage for any grade.
An A* (or a grade 9, or a 7) is not always 90%. The mark you need moves from session to session.
Why? Because some papers turn out harder than others. Boards adjust the boundaries so a grade means the same thing regardless of which paper you happened to sit.
Imagine two students of the same ability, sitting in different years:
A harder paper
Student scores 65/80
Boundary for A: 58/80
Result: Grade A
An easier paper
Student scores 72/80
Boundary for A: 70/80
Result: Grade A
Both earned an A even though their marks differ, because the boundary moved with the difficulty of the paper. This principle is called "comparable outcomes" — making sure a grade carries the same meaning across sessions and years.
How Are the Boundaries Decided?
The exact formulas are not public, but the process across the major boards follows the same shape:
Look at the marks and the evidence
How did everyone perform this session, how does that compare with previous years, and how strong was this group of students on the way in (their prior attainment)?
Senior examiners review real scripts
Experienced examiners read actual answers near each proposed boundary and ask, "Is this the standard of work we expect for an A? For a B?" Statistics give a starting point; human judgment checks it.
The boundaries are confirmed and published
Once agreed, the boundaries are applied to everyone's marks and published alongside (or shortly after) results.
Anyone claiming to know a "secret formula" that predicts exact boundaries is guessing. Boards combine statistical models with expert review, and the details are not published.
Board by Board: How It Works and Where to Find Yours
The idea is the same everywhere, but the grade scales, the extra detail on your statement, and where to find the official numbers differ by board.
Cambridge (CAIE) — IGCSE, O Level, AS & A Level
IGCSE and O Level are graded A*–G; full A Level is graded A*–E, while AS Level is graded A–E (there is no A* at AS). U means ungraded. Your Statement of Results also shows a Percentage Uniform Mark (PUM), a 0–100 score that tells you where you sat within your grade band. Cambridge uses comparable outcomes and publishes threshold tables per session.
Find them: Cambridge grade threshold tables.
Edexcel (Pearson) — International GCSE & International A Level
Edexcel International GCSEs are graded on the 9–1 scale (9 highest; in the UK GCSE convention, 4 is a "standard pass" and 5 a "strong pass"). International A Levels are graded A*–E and are modular: unit marks are put on a Uniform Mark Scale (UMS) and added up before the overall grade is set. Pearson follows Ofqual's comparable-outcomes approach and publishes boundaries each series.
Find them: Pearson Edexcel grade boundaries.
IB Diploma
Each IB subject is graded 1–7 (7 highest), and the six subjects plus up to 3 core points give a total out of 45. The IB sets subject grade boundaries at each session's grade award, blending statistical evidence with how well work meets the published assessment criteria — so it leans a little more on criteria than pure comparable outcomes. Boundaries can differ between the May and November sessions.
Find them: the IB publishes subject grade boundaries to schools via the IB (ibo.org) documents library — ask your IB coordinator for your subjects.
Turning Your Mark into a Grade
To estimate a grade from a practice paper:
- Find the official boundary table for that exact paper and session.
- See which boundary your raw mark clears — that's your grade for that paper.
- On modular qualifications (like IAL), convert to UMS and add across units first, then read the overall grade.
Using an old session's boundaries on a new paper only gives an estimate. Treat past boundaries as a revision guide, never a promise.
What This Means for You
DO: aim above the boundary you're targeting
If past top-grade boundaries ranged widely, aim comfortably higher so a slightly harder paper can't cost you the grade.
DO: focus on understanding, not the numbers
Students who genuinely master the content don't need to worry about where the boundary lands.
DON'T: assume last year's boundaries will repeat
Every paper is different, so every session's boundaries are different.
DON'T: try to "game" the boundaries
There's no shortcut — solid preparation beats boundary-watching every time.
Frequently Asked Questions
What is a grade boundary?
A grade boundary (also called a grade threshold) is the minimum mark you need for a particular grade in a specific exam paper or subject. Score on or above the boundary and you get that grade. Boundaries are published by the exam board after each session, once marking is finished.
Why do grade boundaries change every session?
Because papers vary in difficulty. Boards adjust the boundaries so a grade means the same thing whichever session you sat: a harder paper gets slightly lower boundaries, an easier paper slightly higher. That principle is called 'comparable outcomes'. It's why an A* is not a fixed percentage.
What mark do I need for an A* or a grade 9?
There is no fixed number. The mark for the top grade changes each session with the difficulty of the paper, so it might be in the high 70s one year and the high 80s another. Past boundaries are a useful guide for revision targets, but they never guarantee next session's mark.
Where do I find the official grade boundaries?
Cambridge publishes IGCSE, O Level and A Level threshold tables on cambridgeinternational.org; Pearson publishes Edexcel International GCSE and International A Level boundaries on qualifications.pearson.com; the IB publishes subject grade boundaries to schools through the IB documents library. Your school's exams officer can also give you the boundaries for your papers.
How do I turn my raw mark into a grade?
Find the official boundary table for that paper and session, then see which boundary your raw mark clears. On modular qualifications like International A Level, marks are first converted to a Uniform Mark Scale (UMS) and added across units before the overall grade is decided. Using an old session's boundaries on a new paper only gives an estimate.
Key Takeaways
- Boundaries are not fixed — they move with paper difficulty every session.
- Boards use data plus expert script review — the exact formula is not public.
- Every board does this, on its own grade scale (A*–G, 9–1, or 1–7).
- Best strategy: master the content and aim comfortably above your target grade.
A Bit More Detail (For the Curious)
You don't need any of this to do well — it just shows the thinking behind the numbers.
The "difficulty factor" idea
If this session's paper was harder than usual, the average mark drops. Boards use signals like that to nudge the boundaries down so students aren't punished for a tough paper (and up for an easy one).
A rough way to picture it: if students scored about 10% lower than normal on a paper of the same standard, the boundaries would come down by a similar amount. The real method is more careful than this, but that's the intuition.
Prior attainment
Boards also consider how strong this year's students were before the exam (for example, their earlier results). If a group is genuinely stronger, more top grades can be justified; if not, the boundaries hold. This stops results drifting up or down just because one paper was easier or harder.
Expert judgment has the final say
Statistics suggest a boundary; senior examiners then read real scripts at that mark to check the work truly matches the grade. The published boundary is where the numbers and the expert judgment agree.
Official Sources
- Cambridge International — grade threshold tables
- Pearson Edexcel — grade boundaries
- IB (ibo.org) — subject grade boundaries via your IB coordinator
- Ofqual — comparable outcomes explained
This guide is for revision support. For your own results and the boundaries that apply to your papers, your school's exams officer (or IB coordinator) is the definitive source; the official board pages above are the authority for published boundaries.