The Truth About Interest Rates (And How Banks Make Money)

Have you ever been told that borrowing at 4% and earning 5% is “only” a 1% difference? Here’s the part most people never hear: that 1% difference is actually a 25% return. 

And that one misunderstood truth explains exactly how banks make money—and how everyday people could be using the same math to their advantage. You need to know The Truth About Interest Rates!

Why This Feels So Confusing

On the surface, going from 4% to 5% doesn’t look like much. Most of us were never taught to think beyond the percentage itself. We don’t typically use financial calculators, and even if we do, the math often feels hidden behind buttons and formulas we don’t fully trust.

Yet once you can see all the numbers at the same time, the truth becomes impossible to ignore.

So let’s slow this down and unpack it together—no finance degree required.

How Is Going from 4% to 5% a 25% Return?

Let’s look at the math plainly.

If the Present Value is 4% and the Future Value is 5%, and that change happens over one year (because interest rates are always quoted annually), what is the increase? Many people would say it’s a 1% increase, right? 

Now here’s the key insight: That increase of 1 is 25% of 4.

So even though the spread is 1%, the rate of return is 25%. And this logic holds no matter the scale.

If you borrowed at 8% and earned 10%, the spread is 2%. Yet the return is still: 2/8 = 1/4 = 25%

The volume of interest earned may be different, yet the rate of return stays the same. And this thinking is how banks can give you a savings rate of one thing and a loan rate of another that don’t seem too disparate, yet actually earn them a GREAT return.

Think in Dollars (Because That’s How Real Life Works)

If percentages feel too abstract, switch to dollars.

Imagine borrowing $4 and investing it in something that returns $5. Your profit is $1.

That’s a 25% return on your original $4. You’ve earned 1/4 of what you invested, not 1%. The same is true if you invest $4,000 and end up with $5,000.  When we’re talking rate of return, interest rates (like your savings rate or loan rate), work the same mathematically.

The problem isn’t the math—it’s how rarely we’re shown the math in a way that makes sense.

This Is How Banks Actually Make Money

This simple (and often hidden) truth is the foundation of the banking system. And you might think it doesn’t matter, yet here’s where things get really interesting.

Let’s compare two different time periods—both with the same interest rate spread.

Banks in the 1980s

Banks paid about 9% on Certificates of Deposit and charged about 15% on consumer loans. That’s a 6% spread.

And the return? That spread produced a 66.67% profit for the banks. Yet the average consumer is none the wiser because we’re not trained to think about percentages that way.

Banks in the 1990s

Later, interest rates dropped. Banks paid just 3% on CDs and charged 9% on loans. Still a 6% spread.

Yet the rate of return exploded to 200%.

Why? Because their profit was now twice what it cost them to acquire the money in the first place. In other words, they earned that 3% back twice over. It actually benefited banks to lower rates like that.

Same spread. Wildly different results.

And here’s the kicker: if banks wanted to earn that same 200% return while paying 9% on CDs, they’d have to charge 27% on loans.

That math checks out every time.

The Math from a Business Owner’s Perspective

Let’s step away from banks for a moment. Imagine you own a hardware store.

• A hammer costs you $9

• You sell it for $15

• You make $6, which is a 66.67% profit

Now imagine your supplier drops the cost to $3 per hammer. You can now make 3 more transactions with customers for the same investment, so you extend those savings to them, and YOU only charge $9.

In both cases, you’re only making $6 per hammer. However, with a single investment of $9, you have the ability to either:

• Net $6 by selling one $9 hammer at $15
• Net $18 by selling three $3 hammers at $9

Same profit per hammer. Radically different return on the same capital. (And sure, you could still sell the $3 hammers at $15, yet what happens when your competitors change their prices?)

This is exactly how banks think.

What This Means for You

Here’s the part most people miss: your money has a cost, even when it’s “your own.”

Corporations obsess over the cost of capital. Banks live and breathe it. Yet everyday people? We’re rarely taught to think this way.

We’re told to focus on interest rates instead of rates of return. We’re encouraged to give up control of our savings instead of optimizing it. And we’re almost never shown how to position our money so it keeps working—even while we use it.

This is where strategies like using life insurance as a savings and liquidity tool start to make sense—not as a product, but as a function. A place where money can grow, remain accessible, and continue earning—even while you borrow against it.

Once you understand how banks think, you can start acting like one.

The Real Moral of the Story

The most important thing to watch isn’t the interest rate—it’s opportunity cost and the cost of capital.

When you understand how returns actually work, you stop asking, “Is this a good rate?” and start asking,
“What is this money really costing me—and what could it be doing instead?”

That shift alone can change how you save, borrow, and build wealth for the rest of your life.

And once you see it… you can’t unsee it.

If you’re ready to start warehousing your wealth where it can do the most for you and your family,let’s talk about whole life insurance!