29. Having regard to the advantages the taxpayer obtains under these facilities, the further interest amount can only be properly characterised in these circumstances as a cost incurred for the purpose of enabling a reduction in the principal amount outstanding under the private account. We do not consider the further interest amount is a 'cost of ownership' of the relevant investment asset for the purposes of subsection 110-25(4).
30. We are also of the view the further interest amount cannot be regarded as 'interest on money you borrowed to acquire the asset' for the purposes of paragraph 110-25(4)(a). When interest on an investment account is capitalised, interest incurred on the investment account accrues both in respect of the original principal sum and in respect of the unpaid interest (the 'further interest amount' referred to in paragraph 7 above). All interest accruing retains its character as interest and never becomes part of the principal sum (see Bank of New South Wales v. Brown (As Official Liquidator of Tom the Cheap (WA) Pty Ltd (In Liquidation)) (1983) 151 CLR 514 ('Tom the Cheap'). The further interest amount is not interest on money borrowed but is interest on interest.
31. Interest on the principal sum is a cost of ownership of the asset. Such interest is also 'interest on money you borrowed to acquire the asset' within paragraph 110-25(4)(a).