Investors often debate interest-only versus principal-and-interest as though one is always superior. In reality, each structure solves a different problem. Interest-only can preserve cash flow and direct surplus cash toward non-deductible debt or an offset, while principal-and-interest steadily reduces the loan. The tax, cash-flow and behavioural consequences should all be considered.
- Interest-only improves required cash flow
- Principal does not fall during the IO period
- P&I can reduce long-term interest
- Reversion repayments can jump
- Consider deductible and non-deductible debt together
What interest-only changes
During the interest-only period, scheduled repayments generally cover interest without reducing principal. That keeps required repayments lower, but the balance remains higher for longer.
At the end of the interest-only term, the loan may revert to principal-and-interest over the remaining term, causing a noticeable repayment increase.
Why some investors prefer P&I
Principal reduction increases equity and can reduce long-term interest cost. P&I rates can also be lower than interest-only rates depending on lender pricing.
For borrowers who do not have a productive use for the cash-flow difference, P&I can impose useful repayment discipline.
Think at portfolio level
An investor with a large owner-occupied mortgage may value keeping investment loans interest-only while directing surplus cash to non-deductible home debt. Another investor with no home debt may prefer to reduce investment principal.
Tax outcomes depend on individual circumstances, so loan strategy should be coordinated with tax advice rather than driven by a generic rule.
Frequently asked questions
Is interest-only always better for tax?
No. Tax deductibility depends on the use of borrowed funds and individual circumstances, not simply the repayment type.
Can I extend an interest-only term later?
Possibly, but it generally requires a new assessment and lender approval.
Will interest-only reduce borrowing capacity?
Lender servicing methodology can make IO commitments more demanding, so it should be modelled before application.