From what I've read, they are fairly accurate when you get above 90. It's about a max of +/-1 off your real ATAR. If you skim through this thread, some members have written their AtarCalculator and Matric Calculator marks along with their real ATAR, so you can see the discrepancies.
atar calculators should only be used as a guide and are rarely 100% accurate
THis is because every year subjects scale differently to previous years
Also the marks you put in probably wont be what youll get come december(or when the fuck ever) so theres that aswell
If you really want to see some real examples go to the past hsc results page and occasionally
people will show what the calculator predicted and what they actually got
9/10 it was not the same (sometimes within +- 1.5 atar points but rarely the same)
i would think its different since the marks have not been aligned yet. So your atar would be much higher probably.
The Atar calculators are only useful once you get the aligned/moderated HSC marks from BOS, not raw marks.