What Is an Interest Rate?

In December 2025, the Federal Open Market Committee held the federal funds rate target at 3.50 to 3.75 percent, the direct result of an aggressive rate-hiking cycle that began in 2022 to cool the fastest inflation in four decades.¹ By June 2026, the average 30-year fixed mortgage sat at 6.47 percent.² If you bought a home in 2021 at 3 percent and tried to refinance today, the difference between those two numbers would cost you more than six figures in extra interest over the life of the loan. That is what an interest rate actually is: the price of money, and when that price moves, it moves everything.

The mechanism: how the price of money gets set

Let's start with how this machine actually works. An interest rate is the annual charge a lender applies to a loan, expressed as a percentage of the principal, the amount you actually borrow.³ Borrow $10,000 at a 5 percent rate and you owe $500 in interest for the year. Simple. What is not simple is who decides that 5 percent, and why it is 5 percent instead of 3 or 8.

The answer starts at the Federal Reserve. The Fed's Federal Open Market Committee (FOMC) sets the federal funds rate, which is the overnight lending rate between banks. When one bank needs to cover its reserve requirements for the night, it borrows from another bank at or near this rate.¹ The Fed does not directly set your mortgage rate or the interest on your credit card, but it does not need to. When the cost of overnight money rises, banks pass that cost upstream: short-term rates like those on credit cards follow almost immediately, and long-term rates like mortgages adjust more slowly as the bond market reprices future expectations.

There is a second layer worth knowing: the federal funds rate is not the only lever. The Fed also pays banks interest on reserve balances (known as IORB, interest on reserve balances) and sets an upper boundary called the interest on reserve balances rate to keep the funds rate within its target range. These are the plumbing details, but the takeaway is the same: the Fed's policy decisions set the floor, and market forces, risk, and competition build the rate you actually see on your loan documents.

APR and APY: the two numbers that matter

Here is where most explanations skip a step. There are two rates you will encounter on almost every financial product, and they measure different things.

The Annual Percentage Rate (APR) is the cost of borrowing expressed as a yearly figure, and it includes more than just the stated interest rate: it folds in lender fees, points, and other charges, so it gives you a more complete picture of what a loan actually costs.⁴ The CFPB requires lenders to disclose the APR on loan documents, which is why your mortgage paperwork shows both a rate and an APR that is usually a bit higher.

The Annual Percentage Yield (APY) is the flip side: it measures the return on savings or an investment, and it accounts for compounding, the process of earning interest on interest you have already earned. A savings account advertised at 5 percent APR paying interest monthly actually delivers a 5.12 percent APY because each month's interest earns a little more the following month. Banks advertise APY on savings products because the number is larger and more attractive; they advertise APR on loans because that number is lower. Both are technically accurate. You just need to know which side of the ledger you are on.

What moves your rate

Now shift to where the policy rate becomes your rate. The Fed sets a floor, but the rate you are offered is a product of several forces working at once.

Credit score is the biggest variable you control. A borrower with a 750 score might receive a mortgage rate around 6.5 percent today, while a borrower at 650 might face something closer to 7.5 percent or higher, because the lender is pricing in the additional risk of default.⁵ That difference is not cosmetic: it compounds across 30 years into real money (see the example below).

Loan type matters because different products carry different risk profiles. A 30-year fixed mortgage is priced differently than a 5-year adjustable-rate mortgage (ARM), which is priced differently than an unsecured personal loan or a credit card. The longer and riskier the loan, the higher the rate.

Loan term also shifts the rate. A 15-year mortgage typically carries a rate 50 to 75 basis points lower than a 30-year mortgage because the lender gets repaid faster and carries the risk for a shorter period. A basis point is one one-hundredth of a percentage point, so 75 basis points equals 0.75 percent.

Competition is the underappreciated factor. Banks, credit unions, and online lenders all compete for your business, and the spread between the best and worst offers in the market at any given moment can be wide. Shopping two or three lenders before committing is one of the highest-return uses of two hours in personal finance.

Why this reaches your wallet: the $72,000 example

Abstract rate differences become concrete when you run the numbers. Take a $300,000 30-year fixed mortgage at two rates that are well within the realistic range today.

At 6.5 percent, the monthly principal and interest payment is $1,896. Over 30 years, you pay $682,560 in total, meaning $382,560 of that is interest on top of the $300,000 you borrowed.

At 7.5 percent, the monthly payment climbs to $2,098 and total payments over 30 years reach $755,280, meaning $455,280 in interest paid.

The difference between those two rates is exactly one percentage point. The difference in total interest paid is roughly $72,720. That is a number worth sitting with: a single point on a common mortgage amount costs more than most people earn in a year, paid slowly and invisibly in monthly installments across three decades. Run the numbers for your own loan at the mortgage calculator at /tools/mortgage.

Fixed vs. adjustable: the rate you lock in vs. the rate that moves

While both product types involve interest rates, they manage risk in opposite directions.

A fixed-rate mortgage locks your rate for the life of the loan. If you close at 6.47 percent today, that is your rate in year one and in year twenty-nine, regardless of where the Fed moves. You trade the possibility of a lower rate later for the certainty of knowing exactly what you owe every month.

An adjustable-rate mortgage (ARM) starts at a lower fixed rate for an initial period, typically 5 or 7 years, and then resets periodically based on a reference index such as the Secured Overnight Financing Rate (SOFR). A 5/1 ARM might open at 5.8 percent today, a meaningful savings against the fixed rate, but in year six it adjusts annually and can move substantially if the underlying index rises. ARMs transfer the risk of rate movement from the lender to the borrower. They make sense in specific situations: if you are confident you will sell or refinance before the fixed period expires, or if you believe rates will fall materially before the reset. They carry real exposure if neither of those conditions holds.

The CFPB notes that comparing an ARM's APR to a fixed loan's APR is particularly tricky because the ARM's APR does not reflect the maximum rate the loan could reach.⁴ Compare the initial rate, the index, the cap structure, and the worst-case scenario before choosing.

Overall, money has a price and you pay it everywhere

The interest rate is not background noise in your financial life: it is the mechanism that prices every loan you take and every dollar you save. The Fed moves the floor, your credit history moves your position on the rate spectrum, the loan type and term shape the product, and the compounding math turns small percentage differences into tens of thousands of dollars across time. Understanding how the machine works does not give you the power to override the rate environment, but it does give you the power to make better decisions within it: to shop lenders, to understand what APR and APY are actually telling you, to weigh fixed certainty against ARM flexibility with clear eyes.

One percentage point is the difference between comfortable and stretched for a lot of households. Know what you are signing.