Interest paid is usually the largest tax deduction against rental property income, and in a lot of cases creates an overall loss, which may lead to an overall reduction in income tax payable. Taking out a loan to buy an investment property and claiming the interest charged as a tax deduction seems to be a simple proposition, however, as with anything in relation to tax, there are some complications. It is crucial to be aware of a few rules, especially when the expectation of tax deduction creating tax savings is one of the main deciding factors in purchasing an investment property.