What's your bank loyalty worth? The better part of $5 billion a year. Well that, of course, is what it's worth to the banks - what it's theoretically costing existing customers who don't shop around.
The story is told in the accompanying graph from the Reserve Bank's head of domestic markets, Marion Kohler.
What it quantifies for the first time is how much more banks are prepared to discount interest rates for new customers, compared with what they charge their existing, loyal customers. And the discount has increased over the past couple of years.
Along with other data distilled from mortgage securitisation figures, it underlines how the banks' advertised standard variable rates are divorced from reality. As a guide to mortgage rates, you may as well study your OzLotto numbers.
The RBA's analysis of the securitisation numbers clearly shows how keen the banks are to attract new mortgages. The average outstanding loan is itself at a substantial discount to the advertised rates, but new loans - those taken out over the past three months - are more than 30 points cheaper again.
With about $1.6 trillion in mortgages outstanding, 30 points represents $4.8 billion a year.
While investor loans are more expensive than those for owner-occupiers, the discount offered for new business is a little greater.
Banks self-securitise mortgages to make them acceptable as collateral for liquidity from the RBA. The detail required by the central bank for such securitisation is proving a rich source for the RBA's data miners.
"Data are currently received each month (with a one-month lag) on 1.6 million individual mortgages, with a total value of around $400 billion," Dr Kohler explained.
"This accounts for about one-quarter of the total value of housing loans outstanding in Australia. Around 100 data fields are collected for each mortgage, covering a broad range of variables including loan characteristics, borrower characteristics and details on the collateral underpinning the mortgage."
Earlier analysis had enabled the RBA to put a figure on what Australians actually pay for their mortgages. The latest work by the domestic markets team indicates how keen the bank is to drill down further into the crucial home loan market.
It also is a reminder to everyone who hasn't checked their mortgage rate over the past year or two that they are paying the "lazy tax". By not regularly checking the market, that "lazy tax" ends up adding scores of thousands of dollars to the average home loan.
The big figure of $5 billion is somewhat theoretical though. If we all shopped around, the banks wouldn't be able to discount loans by as much for new customers.
The bottom line is that, on average, we end up paying about as much as the RBA wants us to pay for money. To make up the average though, people on higher incomes with bigger loans who shop around pay substantially less than trusting, loyal customers - also known as mugs.
In her speech to the Australian Securitisation Forum, Dr Kohler demonstrated that very few borrowers pay the standard variable rate. The single most common principle-and-interest rate is about 4.5 per cent, roughly in line with the banks' "package" rate.
The next most-common rate though begins with 3.9 - the 60-point difference is serious money over the life of a loan.
