Renting at $500 p/w is considerably better for your future servicing than having a $500k owner occ mortgage. Thats more of the interpretation of the above. E.g. in your scenario (assume that CBA calculates all debt, new and existing, @ 7.25% as its more comparable between different lenders) - you can borrow another ~$220k for an investment after you live in the owner occupier. If you rent the owner occupier, its more than $400k+, simply because the 'accommodation' expense is far less when renting vs living in your own place. Essentially living in your own place is sensitised because there's mortgage debt attached to it. Renting isn't, banks don't increase your rental expense in their calculators, they take it as is.