While the Reserve Bank of Australia (RBA) may have held the official cash rate at a record low of 1.5% on Tuesday, borrowers could be punished anyway by rising house prices and the banks’ out-of-cycle rate hikes.

Even though the cash rate hasn’t moved since a 25 basis point cut in August 2016, this hasn’t stopped the banks, which have refused to pass on the full benefit of the Reserve Bank’s record-low rates, in order to offset costs and prop up their profits.

Analysis by The New Daily official data published on Tuesday by the Reserve Bank indicates that the gap between the RBA’s rate and the standard rate banks quote to mortgage borrowers is the widest it has been in 20 years.

Ashton De Silva, an RMIT economist and expert on the housing market, said it was “conceivable” that banks could widen the gap even further in the coming months in response to shifts in the global economy.

De Silva pointed out that the Federal Reserve raising interest rates in the United States and Brexit could make it more costly for Australian banks to lend abroad. These costs would be passed on to Australian owners-occupiers.

At four percentage points, the spread between the official rate (which is still the primary driver of bank funding costs according the Reserve Bank) and the standard variable, (SVR), which banks quote to customers, is dangerously close. This margin is the largest since 1994.

Although the SVR is higher than what most customers pay, it is still comparable to discounted rates.

The good news for mortgage borrowers is that the RBA probably won’t hike rates for a few more months, according to many analysts. However, that won’t provide much relief if the banks push up rates in the interim in response to rising borrowing costs.

Martin North, principal of Digital Finance Analytics said that lenders are likely continue to go after investors as well interest-only borrower borrowers and leave owner-occupier rate relatively unchanged.

“Last year there was a massive race to the bottom in terms of discounts to try to gain volume and share. Many banks dented their margins in the process,” North told The New Daily. “They’ve now got the perfect cover, thanks to APRA’s regulatory intervention, and so I’d expected to see mortgage rates continuing to grind higher, particularly for investors and anyone on interest-only.”

While the Reserve Bank’s cash rate may be the main driver of bank funding costs, it’s not the only driver. Australian banks borrow heavily from foreign currency markets such as New York and London, as well as term deposits.

Today’s owner-occupier mortgage rates have fallen from 2011. This was the year that the RBA cut. Official cash rates have dropped by 70% since then, from 4.75% to 1.5%.

However, the benefits of these cuts aren’t being felt by borrowers due to rising house prices, which are being fuelled in part by low rates. While rate cuts are supposed to give households more disposable income by reducing their mortgage payments, it’s important to remember that interest is only half the mortgage, the other half being principal.

The principal is rising due to higher property prices, particularly in the eastern capitals. This means that mortgage borrowers owe a lot of money to banks, and it will continue to rise regardless of what the RBA does.