HSC scaling explained: how marks become an ATAR

What HSC scaling does

Your HSC mark in a course tells you the standard you reached. It does not say where you stood among all students in the state, because the courses have different candidatures. In 2025 there were 27,767 different enrolment patterns among ATAR-eligible students, and 20,127 of them were taken by one student only. UAC's Technical Committee on Scaling therefore scales each course before the ATAR is worked out.

The aim is stated plainly in the 2025 report: a student should neither be advantaged nor disadvantaged by choosing one HSC course over another. The scaling algorithm estimates what every student's mark would have been if all courses had been studied by all students and all courses had the same distribution of marks. The ATAR itself, and the order in which the aggregates are added up, is covered in the ATAR in NSW.

How HSC marks are scaled, step by step

1. Start from raw marks. The raw HSC mark is the average of the raw exam mark and the raw moderated school assessment. These are not the aligned marks that appear on your Record of Achievement, and they are not reported to students. So the share of students in Band 6 in a course has no effect on the ATAR.
2. Standardise. Marks in each course are shifted so the top mark is the same everywhere, and then standardised to a mean of 25 and a standard deviation of 12 on a 1-unit basis (marks out of 50).
3. Find each course's scaled mean. The model says a course's scaled mean equals the average academic achievement of its candidature, measured by each student's average scaled mark across all the courses they completed. This produces a set of simultaneous equations, which UAC solves each year. The scaled standard deviation is the standard deviation of that overall achievement measure.
4. Set a maximum. The maximum scaled mark in a course is the smaller of 50 and the scaled mean plus a multiple of the course's standard deviation. In 2025 the multiple was 2.46, and it is recalculated every year from English.
5. Scale each mark. A non-linear transformation keeps the scaled mean and standard deviation and holds scaled marks between 0 and 50. Students keep their order in the course.

The result is that the same position in two courses can carry different scaled marks. Scaling is carried out afresh every year, so a course is never permanently "scaled down" or "scaled up".

Scaled marks for maths and science courses, 2025

UAC publishes the scaled mean and selected percentiles for every course. These are on a 1-unit basis, so the top possible mark is 50. The scaled mean is the best single guide to the strength of the field. Chemistry (32.0), Physics (31.0) and Mathematics Advanced (31.9) had stronger fields than Biology (26.2) or Mathematics Standard 2 (23.3), and the Mathematics Extension courses had stronger fields again.

Do not read this table as an HSC mark converter. UAC warns that for each HSC mark there can be a range of raw marks and so a range of scaled marks, and that comparing HSC and scaled marks is "of little value". The point of the table is the relativities between courses. The median student in Mathematics Extension 1 had a scaled mark of 41.5, well above the 23.2 of the median student in Mathematics Standard 2, because they were competing in a much stronger group.

A worked example: same marks, different ATARs

The 2025 report gives two students who sat at the 50th percentile in every one of their courses. Their HSC marks per unit averaged 40.0 each, but their ATARs were 60.00 and 80.00. The difference was the field they competed in: the average scaled mean of the first student's courses was 21.9, against 31.3 for the second. Because the aggregate is the sum of scaled marks, the second student's aggregate was around 314 against around 213 for the first.

You can use the same idea on your own courses. UAC's Table A3 lists the scaled mean of every course, so you can see how strong each field was last year and which of your courses carry the most weight per mark.

Which courses count, and the special cases

• English courses are combined. English Studies, English Standard and English Advanced raw marks are placed on a common scale by NESA, so they are scaled as a single course but reported as separate courses.
• The three main maths courses are not combined. NESA now collects extra information that could place Mathematics Standard 1, Standard 2 and Advanced on one scale. Neither NESA nor the ATAR calculation uses it yet, and UAC says any change will be announced before the first affected cohort starts Year 11.
• Extension courses are scaled from the 2-unit course. The scaled mean and standard deviation of an Extension course come from how those Extension students did in the matching 2-unit course. Mathematics Extension 2 students are measured on Mathematics Extension 1, because they do not sit the 2-unit Advanced paper.
• Science Extension is a weighted average. Its scaled mean is a weighted average across the five groups of students who take it with Biology, Chemistry, Earth and Environmental Science, Investigating Science or Physics.

Common mistakes about HSC scaling

• Choosing a course because it "scales well". UAC says scaling is carried out afresh each year. The scaled mean changes if the quality of the candidature changes, and students in every course achieve high ATARs.
• Thinking scaling punishes easy subjects. Scaling reflects the field, not the content. A course with a weaker field is not worse; the same mark just says less about your rank.
• Using your HSC marks to check your ATAR. You cannot. The ATAR is a rank and raw marks, not aligned marks, are used.
• Expecting to see your scaled marks. Scaled marks are not reported to students. They are an interim step.
• Believing the school or postcode matters. UAC says neither does. Only NESA's marks are used.

Practise first, scale later

Scaling only moves marks that exist, so the marks come first. Sit today's Year 12 Maths, Year 12 Physics, Year 12 Chemistry or Year 12 Biology paper as a short timed paper, 8 questions worth 25 to 35 marks. The results page shows a predicted grade with typical cut-offs, not NESA's. Your results come back as a band, explained in HSC bands explained. HSC results and ATARs for 2026 are released on Wednesday 16 December.

Read next

Australia · HSCHSC Maths: Courses, 2027 Exams and Practice QuestionsHSC maths explained: Standard, Advanced, Extension 1 and 2, the new syllabus first examined in 2027, exam formats, worked questions and free daily trials.