How this thing works

The other day somebody told me that school percentile to HSC mark is on the school website.
So this thing converts your school subject percentile to HSC mark and to aggregated ATAR, and finally to your ATAR based on 2025 SBHS HSC results and UAC Average ATAR aggregated to ATAR rank for 2021-2025.

How this works:

1. You input your percentile within subjects.
e.g. Physics 30/140 = 78.5%

2. The calculator uses piecewise linear interpolation based on historical performance data with points at the 90th, 75th, and 50th percentiles to determine the expected HSC Mark.
e.g. Physics 75% is 84 HSC 77.6 ATAR, 90% is 91 HSC 86 ATAR... 78.5% is around 85.6 HSC 79.6 ATAR

3. Sum and Compare to ATAR table
e.g. 447.8 aggregate = 99 ATAR, 459.4 aggregate = 99.5. So 450 is around 99.10

Is this accurate??

Should be significantly more accurate than other websites requiring arbitrary HSC marks as inputs.
My calculation derives using subject PERCENTILEs from SB historical results - far more accurate than using raw marks to determine anything because e.g. physics

Limitations:
Generally, less accurate when (1) cohort size for a subject is small (2) below 40%, or above 99% percentile for any subjects (3) Atar to rank

Disclaimer: Accuracy not guaranteed.