It’s EXTREMELY important. (In some ways, it’s even more important than your ATAR.)
The UCAT is very important for two main reasons. First, almost half of the medical and dental schools that are open to high school applicants (and that hold interviews) make their interview offers purely on the basis of your UCAT results. In other words, if you don’t get a high UCAT score, you can’t even get an interview, let alone get into the course. And even for the medical and dental schools that consider both UCAT and ATAR when making interview offers, a poor UCAT score is going to majorly reduce your chances of scoring an interview offer.
For these universities, performing poorly on the UCAT means that you don’t even get to show off your ATAR, your hard work in studying, your voluntary work, or your extracurriculars—the door is already closed as soon as you underperform on the UCAT. Even if you get a 99.95 ATAR, if you don’t get a good UCAT score you’re done.
Second, the UCAT is important for actually getting into the course. Once you’ve passed the interview stage, your UCAT score is often used again by universities to help them decide whether or not you should be accepted into the medical or dental program. At some universities (e.g. Monash and UWA), your UCAT score is weighted just as heavily as your ATAR when they make course offers.
To grasp how significant this makes the UCAT, we can break things down from the perspective of time. If your UCAT score and your ATAR are both weighted at 33% (like at Monash and UWA), then the 2-hour UCAT exam is equivalent to a whole year’s worth of study for multiple subjects. If you’re taking four subjects in Year 12, this means that 30 minutes of the UCAT exam is worth the same amount as one whole Year 12 subject— which also means that 15 minutes of the UCAT exam is worth the same amount as a 50% final exam. And this is just assuming that your UCAT result and ATAR are weighted equally. At some universities, your UCAT is considered even more seriously than your ATAR: for example, the Joint Program in Medicine (WSU & CSU) and the Bachelor of Dental Science with Honours (UQ) weight the UCAT heavily but only treat your ATAR as a threshold requirement (meaning that once you’ve achieved the minimum ATAR score, they’re not interested in what ATAR you actually achieved). Some universities won’t even look at your ATAR unless you’ve achieved their required UCAT threshold first—if you haven’t, you’re automatically disqualified for a course offer
If you don’t do well on the UCAT, your number of potential universities in Australia and New Zealand can drop
from around 20 to only around 5.
So again—yes, the UCAT is extremely important!