Over the past two years lenders have been incrementally increasing interest rates on investment loans and loans with interest only repayments (as opposed to principal and interest). As the chart below illustrates, the average interest rate margin between a principal and interest home loan and an interest only investment loan is now 1.04% p.a. As recent as January 2016, interest rates for these loans were virtually identical.
This begs the question, should you switch your investment loan to principal and interest repayments to save approximately 0.47% p.a. in interest costs (i.e. difference between 1.04% and 0.57% in the chart below)?
The conventional wisdom for interest only repayments
The conventional wisdom has always been to set up investment loan repayments as interest only. The rationale for this is it allows you to have better control and flexibility over your cash flow and capital. That is, it frees up more cash flow which you can direct towards the repayment of non-tax-deductible debt (i.e. home loan) or invest in other assets for example. But you could always make principal repayments at any time.
This approach had strong merit whilst interest rates for all loans and repayment types were virtually equal i.e. there was no penalty for repaying interest only compared to principal and interest. However, now this has changed, does it still make sense to have interest only repayments?
Our rule of thumb
I have financially modelled the long-term impact of setting up an investment loan with interest only repayments compared to principal and interest (for people that still have a home loan). Obviously, if you set up your investment loans as interest only, you have more cash flow to repay non-tax deductable debt, as despite the interest rate being higher, the repayment does not include a principal component (only interest).
Here is the rule of thumb that I have determined:
If your total investment debt represents 40% or less of your overall debt, set up your investment loans on interest only repayments. However, if your total investment debt represents 40% or more of your overall (total) debt, then set up your investment loan repayments as principal and interest – subject to the exceptions mentioned below.
The reason this rule of thumb works is because if your home loan is relatively small (compared to your overall debt) then any savings resulting from making extra repayments (i.e. if your investment loans were on interest only it g
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