The Interest-Only Cliff: What Happens When Your IO Period Ends in 2026

I have pulled a lot of loan files in the last two years, and the ones that scare clients most are not the fixed-rate rolls everyone wrote about in 2023 and 2024. They are the interest-only reversions. A fixed-rate cliff is a rate reset: your 1.99 per cent becomes a 6.4 per cent, and the number goes up. An interest-only cliff is a different animal. Your rate might not move at all, and your repayment can still jump by more than a third, because for the first time you are being asked to pay back the money you borrowed, over a shorter number of years than you had planned for. Most people do not see it coming until the letter arrives, because nobody explains the amortisation maths at settlement. This is a guide to that mechanic, why 2026 makes it sharper, and what you actually do about it if your interest-only period ends this year or next.

How interest-only works, and why people use it

On an interest-only (IO) loan you pay the lender only the interest each month for an agreed period, usually three or five years, occasionally ten on an investment facility. You pay nothing off the principal. A $700,000 loan at the start of the IO term is still a $700,000 loan at the end of it. There are two honest reasons to use IO, and one bad one. The first honest reason is tax and cashflow for property investors. On an investment loan the interest is deductible against rental income; the principal is not. So while your loan sits interest-only, every dollar of your repayment is working as a deduction, and your out-of-pocket holding cost is as low as it will ever be. Investors also often prefer to direct spare cash into an offset account against their own home (non-deductible debt) rather than pay down deductible investment debt. That is a legitimate structure, and a good accountant will often recommend it. The second honest reason is a temporary, known squeeze for owner-occupiers: a period of parental leave, a business start-up phase, a renovation, a stretch where you genuinely need lower repayments for eighteen months and have a clear plan to switch back. Used deliberately and for a fixed window, that is fine. The bad reason is using IO to buy more house than you can actually afford on principal-and-interest (P&I) terms, and quietly hoping the problem stays in the future. The problem does not stay in the future. It arrives on a specific date, and in 2026 it arrives with teeth.

The mechanic: why the jump is bigger than a rate move

Here is the part that catches people. When you took a 30-year loan with a 5-year interest-only period, you did not get a 30-year runway to repay the principal. You got 25. The five years of IO are five years where the loan balance does not move. When the IO period ends, the lender takes the same balance and amortises it as principal-and-interest over the remaining term only. So a $700,000 loan on a 30-year term with 5 years of IO reverts to P&I with 25 years left to run, not 30. You are now repaying the full principal over a compressed schedule, and you are doing it at whatever the variable rate happens to be on the reversion date. Two things push the repayment up at once: you start paying principal (which you were not paying before), and you pay it over fewer years than the original loan implied. That is why the jump runs from about 25 per cent on a fresh five-year IO all the way to 30 or 40 per cent when there is less term left to amortise over, even when the interest rate has not changed at all. It is not a rate shock. It is an amortisation shock.

A worked example: $700,000, 5-year IO ending in 2026

Take a $700,000 owner-occupier loan, 30-year term, 5-year interest-only period ending now, reverting to a new-customer variable rate of 6.4 per cent (squarely inside the canon 6.2 to 6.5 per cent band for new owner-occupier variable loans in mid-2026).

• During the IO period, at 6.4 per cent, the interest-only repayment is about $3,733 a month. That is it. Nothing comes off the $700,000.
• On reversion, the same $700,000 now amortises as P&I over the remaining 25 years at 6.4 per cent. The repayment becomes about $4,683 a month.

That is a jump of roughly $950 a month, about 25 per cent, on the rate staying flat. And a fresh five-year IO with 25 years left is the mild end of the range. The jump climbs toward 30 to 40 per cent when there is less term left to spread the principal over: a ten-year IO period leaving only 20 years, or an older loan where the reverting P&I term has dropped well below 25 years. On a $700,000 balance reverting at, say, 6.9 per cent over 25 years, the P&I repayment is about $4,905 a month against an IO cost of about $4,025, still roughly a fifth higher, and the shorter the remaining term, the wider that gap gets. The annual cashflow hit on the base example is around $11,300 of extra outgoing, paid out of after-tax income for an owner-occupier. For a borrower on the 32.5 per cent marginal rate, that is roughly $16,700 of gross income you now need to find that you did not need twelve months ago. Run your own numbers on the home loan repayment calculator before you assume you are fine.

Why 2026 makes this worse than it used to be

Two forces are stacking. First, the reversion rate is higher than the rate that was in the air when most current IO periods were set. A five-year IO period ending in 2026 was written in 2021, when variable rates were near 2 to 3 per cent and everyone assumed the loan would revert into something similar. It is reverting into a 4.35 per cent cash rate world, with owner-occupier variable rates at 6.2 to 6.5 per cent and the majors (CBA, Westpac, NAB and ANZ all passed the three 2026 hikes through in full) showing no back-book mercy. If your IO reversion and a fixed-rate expiry happen to land together, which is common for 2021 vintage loans, you get the rate shock and the amortisation shock in the same letter. Second, extending IO is much harder to get approved now. To extend an interest-only period, the lender re-assesses you as if you were a new borrower. That means the full APRA serviceability buffer, still 3 per cent as I write this (the buffer consultation does not close until 18 July 2026, and the outcome is unknown, so do not plan around a cut). Lenders are testing new and re-assessed borrowers at roughly 9.2 to 9.5 per cent. Worse, when you ask to extend IO, most lenders assess your ability to repay the loan as P&I over the remaining, shortened term at that buffered rate. So the servicing test you have to pass to avoid the payment jump is built around the very payment jump you are trying to avoid. That is the trap. The borrowers who most need to extend IO are the ones least likely to be approved for it.

Your options, ranked honestly

1. Extend the interest-only period

Possible, but harder than it was, and it only defers the problem. You will be re-assessed at the 3 per cent buffer against the shortened-term P&I repayment. If you pass, you buy time; if your circumstances genuinely improved (higher income, a clear investment thesis), it can be the right call for an investor. But every year of extension shortens the eventual P&I term further, which makes the final reversion sharper still. Extending a 5-year IO to 10 years on a 30-year loan means the principal eventually amortises over 20 years, not 25, so the ultimate jump is even bigger.

2. Refinance to another lender

If your current lender will not extend or will not sharpen your rate, refinancing is the obvious move, and the sharpest new sub-80 LVR owner-occupier loans (Macquarie Basic, ING Mortgage Simplifier, Athena) are sitting around 5.74 to 5.99 per cent. Dropping from a 6.5 per cent back-book rate to 5.8 per cent on $700,000 saves real money and softens the P&I transition. One warning specific to 2026: refinance valuations are coming back lower. Automated valuation models ingest the Cotality index, and with national values down 0.4 per cent in June, Sydney down 3.2 per cent for the June quarter and Melbourne down 2.6 per cent, a lower valuation can push your LVR up and knock you out of the sharpest rate tiers, or trigger LMI. Check the numbers on the refinance calculator and read the refinancing walkthrough before you assume the door is open.

3. Switch to P&I voluntarily, early

The unglamorous option that I recommend most often. You do not have to wait for the reversion date to start paying principal. Ask your lender to switch you to P&I now, or make voluntary principal payments while still on IO. Yes, your repayment goes up sooner. But you smooth the transition instead of hitting a wall, you start reducing the balance (so the eventual amortisation is over a smaller number), and you demonstrate repayment capacity that helps if you later need to refinance. For a household that can absorb the P&I payment, switching early is almost always better than riding the IO period to its last day.

4. Sell

The option nobody wants to hear, but for an over-geared investor staring at a reversion they cannot service, selling into a market that is still functioning beats being forced to sell later into a worse one. Sydney and Melbourne are in a confirmed, accelerating correction and auction clearance is in the low 40s, so this is not a "wait for the top" market. If the numbers do not work even after refinancing and switching, decide on your own terms rather than the lender's.

The investor-specific angle: the deduction shrinks as you repay

For property investors there is a second sting. Once you are on P&I, a growing share of each repayment is principal, which is not deductible. Your interest deduction falls every month as the balance drops. So the reversion raises your cash outgoing and simultaneously reduces your tax shield. On top of that, the May 2026 Federal Budget changes to negative gearing and the CGT discount are actively pulling investors out of established stock, which is part of why established-dwelling values are softening. If your investment case only ever worked on maximum deductibility and interest-only forever, 2026 is the year that thesis gets tested. Model the after-tax position honestly with your accountant. Our investment lending page covers the structuring questions worth raising.

What to do six months before your IO period ends

1. Find the exact reversion date and the remaining term. It is in your loan contract or your online banking. Note whether a fixed-rate expiry lands near the same date; if so, you are facing both shocks at once and need to start earlier.
2. Calculate the actual P&I repayment on your current balance over the remaining (shortened) term at 6.4 per cent, not the original 30 years. Use the repayment calculator. Know the real number, not the one you are hoping for.
3. Stress-test it against your budget at the buffered 9.2 to 9.5 per cent, because that is what a lender will do to you if you try to refinance or extend.
4. Get a valuation read early. With AVMs feeding off a falling index, order a refinance quote now so a low valuation does not ambush you at the wire.
5. Ring your current lender first. Ask two things: what new-customer variable rate they would give you at your LVR, and whether they will extend IO. Existing customers often get 0.10 to 0.30 per cent off a retention reprice just by asking, and that costs you nothing.
6. If they will not move, refinance while you still service comfortably. The best time to refinance is before the payment jump lands, not after, when your budget is already stretched and your servicing looks worse on paper.
7. If the numbers genuinely do not work, decide early. Switching to P&I voluntarily, or selling on your own timeline, both beat a forced decision at the reversion date.

The interest-only cliff is not a surprise. It has a date on it, and the maths is knowable today. The households that cope are the ones who ran the real P&I number six months out and made a decision, not the ones who opened the reversion letter and found out at the next direct debit. Do the calculation this week.

Disclosure

Your Finance Guide partners with Australian Lending and Investment Centre (ALG) ACL 505575 for broker matching. ALG receives lender commissions on settled loans. Note that some of the best moves here pay a broker nothing: switching your existing loan to P&I early, or asking your current lender for a retention reprice, earns no commission and is still frequently the right call. When we point you toward those, it is because the file says so, not because it pays.