All ATAR calculators can only estimate a ranking based upon previous HSC scaled data.
Actual ATAR rankings are calculated using raw data which changes each year.
This depends upon the candidature of the students sitting for the each of the HSC exams.
What is the most accurate ATAR calculator?
The most accurate ATAR results are the rankings you receive from the University Admissions Centre (UAC).
All ATAR calculators use HSC scaled data from previous years to estimate a ranking.