IGCSE Chemistry Grade Boundaries Explained

Students chase past-paper percentages without knowing what those percentages buy. A 78% on a June Paper 4 might be comfortably A*; the same 78% on a harder November paper might sit even further above the line. Understanding how 0620 thresholds work turns vague hope into a marks target per paper, and a marks target is something you can train for.

Raw marks vs weighted marks

Your final 0620 grade comes from three papers, and they do not count equally.

Component	Raw marks	Weighting
Paper 1 or 2 (multiple choice)	40	30%
Paper 3 or 4 (theory)	80	50%
Paper 5 or 6 (practical / alternative to practical)	40	20%

Notice the mismatch: the multiple-choice paper is 40 raw marks but worth 30% of your grade, while the practical component’s 40 raw marks are worth only 20%. Cambridge scales each paper’s raw score to its weighting before adding them. A mark on Paper 2 is therefore worth more to your final grade than a mark on Paper 6, which is why coasting through MCQ practice is the quietest way to lose a grade.

Grade thresholds are then published against the weighted total, not the raw total. When you see a threshold document saying A* required 169 out of 200, that 200 is the weighted maximum for that paper combination.

Why boundaries move every series

Cambridge does not run a fixed pass mark. Each series, senior examiners set thresholds using statistical evidence and judgement of the actual scripts, so that a grade represents the same standard of chemistry whatever paper you happened to sit. A harder Paper 4 produces a lower A* threshold; an easier one pushes it up.

The practical consequence: never read one series’ thresholds as a promise. Read three or four recent series and you get a band, not a number. For 0620 Extended, the recent pattern looks roughly like this (indicative figures from published threshold documents, not an official rule):

Grade	Typical weighted range (indicative)
A*	~75-85%
A	~62-75%
B	~50-62%
C	~38-50%

These bands drift series by series. The honest takeaway is the width of the gap: an A* has recently demanded roughly three quarters of the weighted marks, and an A roughly two thirds. Check the official threshold documents on cambridgeinternational.org for the exact figures of any past series.

Core C-G vs Extended A*-E

The two routes are graded on different scales, and this decision caps your ceiling before you write a word.

• Core route (Papers 1, 3, 5 or 6): graded C, D, E, F, G. The maximum grade is a C, no matter how strong the script.
• Extended route (Papers 2, 4, 5 or 6): graded A*, A, B, C, D, E. The scale officially runs A*-G, but Extended papers are designed to discriminate at A*-E; fall below the E standard and the result may be ungraded.

Core thresholds sit at lower percentages than Extended thresholds for the same letter, because Core papers contain only Core content. A C on Core and a C on Extended are the same grade on the certificate, but only Extended leaves the A*/A door open. If you are deciding between routes, our Core vs Extended guide walks through who should sit which, and when a switch is still possible.

June vs November series

Malaysian international schools enter students for the May/June series or the October/November series, and both run the full 0620 assessment. Thresholds are set independently for each, so a November A* boundary can sit a few marks either side of the previous June’s. Neither series is systematically easier. What changes is your preparation runway: a November candidate gets the long mid-year stretch for past papers, while a June candidate revises through the first months of the year. Plan around your series date, not around threshold folklore.

Turning boundaries into a marks target per paper

Here is the exercise we run with students at the start of exam-technique tutoring, and you can do it yourself in ten minutes.

Step 1: pick your target with a safety margin. If recent A* thresholds ranged from 76% to 83% weighted, train for 85%. Boundaries move; your buffer absorbs the movement.

Step 2: convert the percentage into raw marks per paper. For an 85% weighted target on Extended:

Paper	Raw marks	85% target
Paper 2 (MCQ)	40	34/40
Paper 4 (theory)	80	68/80
Paper 6 (ATP)	40	34/40

Step 3: budget the losses, not the wins. The table above says you can afford to drop 6 marks on Paper 2, 12 on Paper 4 and 6 on Paper 6. Suddenly every past paper becomes a diagnosis: where did your 12 Paper 4 marks go? If 8 of them died in mole calculations, that is one fixable topic, not a vague “I need to revise more”. Our breakdown of how to get an A* builds the full strategy on top of exactly this arithmetic.

Step 4: re-run after every timed paper. Mark against the mark scheme, log the gap to target per paper, and watch the gap close week by week.

Worked exam question

Boundaries reward whole-paper discipline, so here is a threshold-flavoured example of how single marks compound.

Q (Paper 4 style): Dilute sulfuric acid is electrolysed using inert electrodes. Name the product at each electrode and give the ionic half-equation at the anode. (3)

Model answer: Cathode: hydrogen (1). Anode: oxygen (1). Anode half-equation: 4OH⁻ → O2 + 2H2O + 4e⁻ (1).

Mark-scheme logic: each line is one raw mark, worth roughly 0.6% of the final weighted grade on Paper 4’s 50% weighting. Three-mark electrode questions like this appear on nearly every Extended theory paper. Drop this question twice across a paper and you have spent half your A* buffer on one topic. That is the real meaning of a grade boundary: it is paid for in 1-mark coins.

The mistakes that cost marks

1. Training to last year’s threshold exactly. Boundaries move a few marks each series. A zero-margin target fails on a hard year; aim 5-8% above the recent band.
2. Ignoring weighting when revising. An hour on MCQ technique moves 30% of your grade; treating Paper 2 as the “easy paper” is how A students land a B.
3. Comparing your Core mock percentage to Extended thresholds. Different papers, different scales. A 70% Core mock does not mean a B: the Core ceiling is C.
4. Treating Paper 6 as separate from the grade. It is 20% of the total. A weak ATP paper drags an otherwise A* script to an A; our Paper 6 guide closes that leak.
5. Reading one threshold document and stopping. One series is an anecdote. Three or four give you the band that actually predicts your target.

The Malaysia note

Malaysian schools split between the May/June and October/November series, and the question we hear most from parents is whether November boundaries are “kinder”. They are not. They are simply set for a different paper. The more useful local habit: ask your school’s exams officer for the threshold documents matching your child’s exact paper combination from the past two years, then set the per-paper targets above. Worried that target-setting sounds like pressure? It is the opposite: a student who knows they can afford to drop 12 marks on Paper 4 walks into the hall calmer than one chasing a perfect script.