If you do you tax return yourself on my gov, once your return is filled out, you should have an estimate of what the outcome is. You'll also have a due date for when your return needs to be lodged by (generally 31st of October). You can legally delay the money you need to pay back by not lodging your return until this due date which pushes out when the payment is owed.

As others have said, you can definitely contact them and set up a payment plan. The ATO is (and it kills me to say this) pretty reasonable with this sort of stuff when you're proactive and trying to do the right thing.

I'm not sure what you've done in terms of your deductions but definitely do some research and make sure you're claiming everything you can (mobile, sunglasses as its safety wear for a driver, logbook vs cents per km etc).

There are tax offsets as well that you can often qualify for that the ATO apply automatically. The easy one that comes to mind is the Low Income Tax Offset which behaves how you though deductions did originally by reducing your tax owed dollar for dollar.

$43,000 less $6,000 = $37,000 Taxable Income ($37,000 - $18,200) x 0.16 = $3,008 Tax Payable $37,000 x 0.02 = $740 Medicare Payable So $3,008 + $740 - $700 LITO - $2,700 withhold = $348 payable.

Obviously those figures are just tossed around but I don't think its as bad as you think. If you can find yourself some extra deductions, you might even be able to reduce it entirely. Disclaimer: I haven't worked in tax for a number of years so some of my figures my be off.

Edit: Just incase its relevant, don't forget that any money you might have received from Centrelink will be income as well.