How central bank interest rates reach your mortgage

HostIt always feels a bit strange when the news starts buzzing about the central bank raising or lowering rates by a tiny bit. It sounds like a math problem for people in suits, until that letter shows up in the mail saying your house payment is going up. How does a choice made by a few people in a stone building downtown actually end up taking money out of a normal person's paycheck?

GuestIt's a long path, but it starts with a simple rule. The central bank is basically the bank for other banks. Your local bank has to keep a certain amount of cash ready every single night. If they had a busy day and lent out too much, they might be short on their numbers. To fix that, they have to borrow money overnight from other banks or from the central bank itself. The rate you hear about in the news is the price those banks pay to borrow that quick cash. When that price goes up, it becomes more expensive for your bank to stay in business. They're not just going to eat that extra cost themselves. They pass it on to you by charging more for the loans they give out, like the one for your house.

HostWait, why does a bank even need to borrow money from anyone else? They have all our savings sitting in the vault. It seems like they should've more than enough to cover things without needing a loan every night.

GuestYou would think so, but banks don't just let your money sit in a big pile. They put it to work. They take the cash you put in your savings account and lend it out to someone else for a car or a new shop. They keep only a small slice of it on hand. The problem is that every day is different. Some days more people take money out than they put in. By the time the doors lock at five o'clock, the bank might be a few million dollars short of what the law says they must have in the vault. They borrow that gap for just a few hours until the next morning. If the central bank makes that overnight loan cost more, the local bank looks at all their other business and realizes they need to bring in more cash to cover it. That's why they raise the interest on your mortgage. They're trying to keep their own heads above water and make sure they still turn a profit.

HostSo it's just a chain of people passing the bill to the next person down the line. But that doesn't explain why the rate for my house moves before the central bank even does anything. Sometimes the news just hints that a change is coming, and suddenly the bank is already charging more for a new loan.

GuestThat's where things get really fast. Most people think banks just wait for orders, but they're actually trying to guess the future. Banks and big investors trade what they call bonds, which are basically just promises of future money. If everyone thinks the central bank will raise rates in three months, they start selling those bonds now. This causes the return on those bonds to go up right away. Since a mortgage is a long-term loan, banks look at those bond returns to decide what to charge you. They don't want to give you a loan at four percent today if they think the cost of money will jump to five percent tomorrow. They move their prices early to protect themselves from what they see coming down the road. It's less like a slow wave and more like a crowd of people all running for the door at the same time because someone smelled smoke.

HostThat sounds like a lot of guessing. It feels like my house payment is being decided by a bunch of people who are just nervous about what might happen next year. It doesn't seem fair that a hunch can cost me a hundred dollars a month.

GuestIt can feel that way, but it's how they handle risk. A bank is giving you money today and hoping that thirty years from now, that money is still worth something. They have to bake all that risk into the price. If they think the whole world is about to get more expensive, they raise your rate to make sure they're not losing value over time. There's also the matter of what they call the spread. The bank wants to make sure there's a gap between what they pay to get money and what you pay them. If that gap gets too small, the bank stops making money and could even go bust. They're constantly tweaking your rate to keep that gap just wide enough to stay safe.

HostBut when the central bank drops the rates to help the economy, it feels like my bank is a lot slower to send that letter. They're quick to raise my costs but they seem to take their sweet time when it's time to lower them.

GuestThere's some truth to that. It's much easier for a bank to move fast when it helps their bottom line. But there's also a bit of a clog in the pipe. A bank might be holding a lot of old loans that they funded when money was expensive. They can't just drop their prices for everyone immediately because they're still paying off their own old debts. They also worry that a rate cut might not last. If they lower your mortgage rate and then the central bank changes its mind a month later, the bank is stuck with a lower profit for years. They wait for a clear sign that the trend is real before they commit to giving you a better deal.

HostThe bank is essentially a middleman trying to stay one step ahead of a moving target.

GuestThe bank is always balancing on a tightrope between the tiny price of money they pay tonight and the huge, long-term bet they're making on your house for the next few decades.

HostThat bank letter in the mail makes a lot more sense now that I know they're just pushing their own daily bill for cash down to my front door.