In today’s episode of Wealth Coffee Chats, Sarah Shome from Positive Money pulls back the curtain on one of the most misunderstood parts of lending: how banks actually set your interest rate. If you think the banks just wait for the Reserve Bank of Australia (RBA) to move and then follow suit, you’re only seeing half the picture. Sarah explains the “Bank Bill Swap Rate” (BBSW), why banks “buy” money from you, and how fixed rates are actually a prediction of the future rather than a reflection of today. If you want to know how to better negotiate a rate discount, you need to understand the math the banks are using in the back end.

What We Covered:

• The Two Parts of an Interest Rate: Every rate is essentially Cost of Funds + Bank Margin.

• Banks “Buying” Money: How your high-interest savings accounts and term deposits are actually the bank purchasing the capital they eventually lend out.

• The BBSW (Bank Bill Swap Rate): The “hidden” rate at which banks sell money to each other every morning between 8:30 AM and 10:00 AM.

• Out-of-Cycle Moves: Why your rate might go up even if the RBA stays on hold (and why the BBSW is usually to blame).

• Lender Margins: A reality check on bank profits—why asking for a massive 0.8% discount might be impossible if the bank’s margin is already thin.

• Fixed vs. Variable: Why variable rates are about the “now,” while fixed rates are based on “Swap Rates”—the market’s best guess of where rates will be in 3 to 5 years.

• The Timing Myth: Why trying to “time” a fixed rate is impossible because the market has usually priced in the news before you even hear it.

3 Key Takeaways

1. The RBA Sets the Tone, Not the Price: The RBA’s cash rate is the foundation, but the BBSW is the actual market price. If the cost for banks to swap money rises, your mortgage rate follows, regardless of what the RBA does.

2. Fixed Rates are “Future” Rates: A fixed rate isn’t a reflection of today’s economy; it’s a reflection of where the market thinks the economy is going. If fixed rates are dropping while variable rates are high, the market is betting on future rate cuts.

3. Know the Margin to Negotiate: Banks have operating costs and reserve requirements. Understanding that a bank might only be making a ~2% margin helps you realize why there is a “floor” to how much of a discount they can realistically offer.