Why 60% is an A in one session and a B in the next

7 min read · updated 10 October 2026

A mark on its own means nothing

You finish a past paper, mark it, and score 90 out of 150. Is that good? The honest answer is that nobody can tell you from the number alone — not your teacher, not a website, not the examiner. 90 out of 150 has been an A in one session and a B in another, on the same subject.

That is not unfairness. It is the system working as designed.

What boundaries actually are

Every exam is slightly harder or easier than the last, however carefully it is written. A question that looked straightforward on paper turns out to confuse half the country; a topic everyone expected does not appear.

If the grade required a fixed percentage, a student would be punished for sitting the year the paper happened to be hard. So instead, after every single sitting, Edexcel looks at how students actually performed and sets the mark needed for each grade for that paper. A harder paper gets lower boundaries. An easier one gets higher boundaries.

The grade is meant to represent the same standard of work every year, even though the mark that earns it moves.

How much do they move?

Enough to matter. It is common for an A boundary to shift by five or six marks between sittings, and a swing of ten is not unusual. On a 150-mark paper that is the difference between two grades for a student sitting near a boundary.

This is why a rule of thumb like "80% is an A" is worse than useless. It will tell some students they are safe when they are not.

The difference between IGCSE and International A Level

These two work differently, and confusing them is a common mistake.

International GCSE is marked on raw marks. You score what you score, and the boundary is published as a raw mark out of the paper total. To know your grade you compare your mark against that session's table.

International A Level uses something extra: the uniform mark scale, or UMS. Your raw mark is converted to a standardised score out of a fixed maximum, and it is the UMS total across all your units that determines the grade. This is what allows units sat in different sessions, against papers of different difficulty, to be added together fairly.

In practice, for IAL you are usually working against roughly 80% of the uniform marks for an A and 90% for an A*, with the raw mark needed to reach that moving session by session.

Reading your own mock mark honestly

Three things worth doing, in order:

• Mark against the official mark scheme, not your memory of what you meant. Marks are awarded for specific points, and generous self-marking is the most common reason a student is shocked on results day.
• Compare against the boundaries for the session that paper came from, not the most recent one. The grade calculator on this site does that for you.
• Look at the gap, not the grade. "Nine marks short of a C" tells you what to do next. "Got a D" does not.

What the calculator here does

Enter your mark and the paper, and it shows where you fall against the real published boundaries, and how many marks separate you from the next grade up. It is an honest estimate of where you stand on that paper — nothing more. It cannot predict your result, because your result depends on a paper that has not been written yet and boundaries that have not been set.

Used properly, it answers the only question that matters during revision: not "what grade am I", but "how far have I got to go, and in which subject".