Mortgage 101: The One About Interest Rates

If I had a dime for every time I'm asked about mortgage rates...let's just say I wouldn't be writing this. I'd be on a beach with a mojito in my hand.

“Rates went up.”

“Rates came down.”

“What’s the rate today?”

“My friend got a 4.99%.”

Cool, cool, cool...but before any of those sentences are actually useful, we need to understand what a mortgage interest rate is—and, just as importantly, what it isn’t.

Because “the rate” is only one piece of the cost of borrowing money.

First, a tiny bit of mortgage vocabulary

When you borrow money to buy a home, the amount you actually borrow is called the principal.

Let’s say you buy a $200,000 house and put $10,000 down. Ignoring other financing details for the moment, you would borrow $190,000.

That $190,000 is your original principal balance.

As you make payments over time, part of your payment goes toward interest and part goes toward reducing the amount you still owe. So your principal balance gradually gets smaller.

On a typical fixed-rate mortgage, that happens through something called amortization. Early in the loan, more of your payment goes toward interest because your outstanding balance is larger. As the balance comes down, less interest is due and more of that payment begins going toward principal.

And one quick distinction because mortgage terminology loves making perfectly normal things confusing: your principal balance and your payoff amount are not necessarily the same number.

If your statement says you owe $287,000, that does not mean a check for exactly $287,000 would necessarily make the mortgage disappear today. Your payoff amount also includes interest owed through the actual payoff date and may include other outstanding charges.

So: principal is the money you borrowed and still owe. Interest is the price you pay for borrowing it.

Now we can talk about the rate.

What the interest rate actually does

Your mortgage interest rate determines how interest is charged on the money you borrowed.

If your promissory note says your interest rate is 6.5%, that is your note rate. It is the actual interest rate written into the loan agreement. That rate is one of the major ingredients used to calculate your monthly principal-and-interest payment.

Notice I said principal-and-interest payment, not necessarily your entire housing payment.

Your total monthly mortgage payment may also include property taxes, homeowners insurance, and mortgage insurance, depending on your loan and whether those amounts are being collected through escrow. Those costs can change even when you have a fixed-rate mortgage because they are not your mortgage interest rate.

This is why I am annoyingly specific about language here. A fixed mortgage rate does not necessarily mean your total monthly housing payment can never change.

It means the interest rate itself is fixed. Different conversation.

Here’s where “What’s the rate?” starts becoming a problem

When people ask me what mortgage rates are, what they usually want is one number. Unfortunately, mortgage pricing does not work that way.

Lenders have a whole range of interest-rate options available at the same time, and each one can come with a different upfront cost or lender credit.

So you might have an option with a lower interest rate that costs more upfront, another option with fewer upfront costs and a slightly higher rate, and several choices in between.

This is why seeing an interest rate online without knowing the assumptions behind it tells you surprisingly little.

That advertised rate may assume a certain credit profile, loan program, down payment, property type, occupancy, loan amount, and—very importantly—a certain number of points being paid upfront.

The rate itself is real. The assumption that it applies to you may be doing some very heavy lifting.

So what are “points”?

Points, or discount points, are upfront costs paid in exchange for a lower interest rate. Or, said another way, the sticker price to essentially 'buy' a lower rate - hence the term "buydown."

One point equals 1% of the loan amount, although you absolutely do not have to buy points in nice, tidy whole numbers.

If you borrow $300,000, one point would be $3,000. Half a point would be $1,500.

Paying points generally means paying more money at closing in exchange for a lower interest rate and lower principal-and-interest payment over time. CFPB describes points as exactly that tradeoff: more upfront, less over time.

And points are neither inherently good nor inherently bad. This is one of those things that gets discussed like there must be a Correct Mortgage Person Answer.

There isn’t.

Sometimes paying points makes fantastic sense. Sometimes it makes absolutely no sense whatsoever.

Does it pencil out and actually save you money? The good news is that the answer boils down to simple math. And my favorite thing about math--is that it never lies.

Let’s say Option A costs $5,000 upfront and has a $2,000 monthly principal-and-interest payment.

Option B costs $6,200 upfront but reduces the payment to $1,986.

You are spending an additional $1,200 today to save $14 per month. $1,200 ÷ $14 = about 86 months.

So it would take a little over seven years of monthly savings just to recover the additional money you spent upfront (to break-even).

Now we actually have something useful to talk about.

Is preserving cash today-or monthly-more important? Do you expect to keep this mortgage longer than the seven years needed to even earn back what the rate cost you?

Could that $1,200 be put to better use somewhere else? If you’d otherwise invest that money, you may have the potential to earn far more in the stock market than you’d save by buying down your mortgage rate. Different risk, obviously—but absolutely worth including in the math.

Is there a different rate option with a much shorter break-even? Or at minimum, one that aligns with your housing/mortgage future?

Those questions matter WAY more than whether somebody announced that one option had “the lower rate.”

You can also move the tradeoff in the other direction

Instead of paying more upfront for a lower interest rate, you can often choose a somewhat higher interest rate and receive a lender credit toward your closing costs.

Same basic tradeoff. Reverse direction.

Less money upfront, higher interest rate. More money upfront, lower interest rate. CFPB describes lender credits and discount points as two sides of that same pricing tradeoff. Again, neither is automatically the better deal.

If you are short on cash at closing, preserving several thousand dollars may be substantially more valuable to you than shaving a small amount each month.

If you have plenty of cash, expect to keep the mortgage for a very long time, and the break-even calculation is favorable, paying additional money upfront may make more sense.

The mortgage does not know which one you value more. That is where strategy comes in.

And then there’s APR

This is where people sometimes try to solve the whole problem by saying, “Fine. I’ll just compare APR.”

If only.

APR—or Annual Percentage Rate—is intended to give you a broader measure of the cost of borrowing by incorporating your interest rate plus certain points, fees, and other finance charges. That is why APR is usually higher than the interest rate itself.

We have an entire separate Mortgage 101 conversation about APR because it deserves one.

For now, just understand this distinction:

Your interest rate tells you the amount you’re being charged for the money you borrowed. APR attempts to account for certain additional costs of obtaining that financing.

They are related. They are not interchangeable.

And APR does not magically eliminate the need to look at the actual numbers underneath the loan.

This is why I hate vague rate quotes

If someone tells you: “My lender quoted me 6.25%.”

I immediately have questions: At what cost? How many points? Any lender credits? What loan program? What down payment? What credit profile? What lock period? When was it quoted?

Because a mortgage interest rate without the pricing assumptions attached to it is incomplete information.

It is a little like telling me something costs $500 without telling me what the thing is. Wonderful. We have a number. Now I need the rest of the data.

When comparing actual mortgage options, I want to look at the rate and the costs attached to getting that rate. CFPB recommends doing the same thing: compare the basic loan terms, then look at points, fees, credits, monthly costs, and the other details that affect what you are actually paying.

Because the lowest interest rate is not automatically the cheapest loan. And the option with the lowest upfront costs is not automatically the cheapest loan either.

It depends on how those two pieces work together over the amount of time you realistically expect to keep the mortgage.

That is the actual decision.

The part I want you to remember:

Mortgage rates are not one universal number that you get to walk in and order off a menu.

Your interest rate is part of the price of borrowing money, and different rate options can come with different upfront costs or credits.

You can often pay more now to pay less over time.

Or you can pay less now and accept a higher cost over time.

And sometimes the smartest option is sitting somewhere in the middle.

So when you see a mortgage rate advertised online—or your neighbor tells you what rate they got—do not stop at the number.

Ask what came with it.

Because “What’s the rate?” is only the beginning of the conversation.