If you could save $x per year but it could you $y one off, how much bigger to y does x have to be? e.g. Sell a $800,000 investment property and free up $400,000 in cash, use the cash to pay down the main residence loan, reborrow $400,000 to invest. Something like this may increase tax deductions by $400,000 x 5% = $20,000 pa. This may put $10k in your pocket each year as well as compounding effects. But the fees of selling may be say $20,000 So would it be worth spending $20,000 once off to save $10k per year? You would make your money back in 2 years and thereafter it would be all savings. I think that would probably be worthwhile. But what if the costs were $40,000 and it took you 4 years? The expenses would be mainly CGT, but may also be stamp duty, and conveyancing costs for a transfer between spouses and I am trying to work out at what point it would be worth doing. What do you think?