Interest Rates and the Rental Price of Capital: How Firms Decide What to Build

A logistics company is weighing a new distribution center. The building, racking, and automation will cost $10 million up front and is expected to throw off about $1.4 million a year in added profit for a decade. Good idea or bad idea? The honest answer is: it depends entirely on the interest rate. At 4 percent the project is clearly worth building. At 9 percent it quietly destroys value. The asset is identical in both cases. What changed is the price of the capital it ties up.

That price is the interest rate, and understanding it as the rental price of capital - rather than just a number on a loan - is the key to how every serious investment decision actually gets made.

The interest rate is a rental price

When a firm sinks $10 million into a building, that money is no longer available to do anything else. It could have been lent out, paid to shareholders, or invested in a different project. The interest rate measures what those funds could earn elsewhere - their opportunity cost. So the interest rate is, in effect, the rent on capital: the price of using $1 of capital for one year (Interest - Econlib).

This is why economists treat the interest rate as the hurdle every project has to clear. If a firm can earn 7 percent risk-adjusted by doing nothing unusual with its money, then a new project had better return more than 7 percent, or the firm is destroying value by tying its capital up in something that earns less than the going rate.

Real-world rates are easy to find. The cost of borrowing for a creditworthy company tracks corporate bond yields - the Moody's Aaa and Baa series, for instance, are published continuously by the Federal Reserve (Moody's Seasoned Aaa Corporate Bond Yield - FRED). The 10-year Treasury yield serves as the risk-free anchor that nearly every other rate is built on top of (10-Year Treasury Constant Maturity Rate - FRED).

The idea in plain words: discounting

The tool firms use to turn "it depends on the rate" into an actual decision is net present value (NPV). The idea is simpler than the name.

A dollar next year is worth less than a dollar today, because today's dollar could be invested and grow. If the relevant rate is 8 percent, a dollar one year out is worth about 93 cents now - you would only need to set aside 93 cents today to have a dollar in a year. To value a stream of future cash flows, you "discount" each one back to today using the interest rate, then add them up. Compare that total to the up-front cost. If the discounted value of the future cash exceeds the cost, the project has positive NPV and is worth doing. If not, it isn't.

The rate you discount with is not arbitrary. It should be the firm's cost of capital - the blended cost of the money funding the project, weighing what it pays lenders against the return its shareholders require. That blended rate is the project's true hurdle.

Walk through the numbers

Take the distribution center: $10 million today, then $1.4 million a year for 10 years. Here is the NPV at three different costs of capital.

At a 4 percent cost of capital, the future profits are worth $11.36 million in today's terms - comfortably more than the $10 million price tag - so the project adds about $1.36 million of value. Build it.

At 7 percent, the same $1.4 million-a-year stream is worth only $9.83 million today, just shy of the cost. NPV turns slightly negative. The project is a coin flip that leans no.

At 9 percent, the future cash is worth only $8.98 million against a $10 million cost - a $1 million destruction of value. Kill it.

Notice what did the killing. The cash flows never changed. The building is the same. Higher rates simply made the distant dollars worth less today and raised the bar the project had to clear. Somewhere between 4 and 7 percent lies the project's internal rate of return - the discount rate at which NPV hits exactly zero, the break-even hurdle. Above that rate, don't build; below it, build.

Change one thing: when the Fed moves

This is not an abstraction - it is the exact channel through which monetary policy works. The Federal Reserve sets a target for the federal funds rate, the overnight rate banks charge each other (Federal Funds Effective Rate - FRED). That rate ripples outward into the daily structure of borrowing costs the Fed publishes in its H.15 release (Selected Interest Rates (H.15) - Federal Reserve), and from there into corporate bond yields and the cost of capital firms actually face. The Fed adjusts this rate through open market operations (Open Market Operations - Federal Reserve).

When the Fed raised rates sharply in 2022-2023, the cost of capital for businesses jumped. Projects that penciled out at a 4 percent hurdle suddenly had to clear 7 or 8 percent - and a wave of them, like the distribution center above, flipped from positive to negative NPV. Firms shelved or delayed them. That deliberate cooling of business investment - and, through the same mechanism, the housing market via the 30-year mortgage rate (30-Year Fixed Rate Mortgage Average - FRED) - is precisely how higher rates slow an overheating economy. The aggregate result shows up in the national accounts as a slowdown in gross private domestic investment (Gross Private Domestic Investment - FRED).

What this means for your decisions

The NPV-versus-hurdle-rate logic is not just for corporate finance departments. The same discipline applies to a landlord deciding whether to add a rental unit, a self-employed person weighing a $15,000 piece of equipment, or anyone choosing between paying down a loan and investing. In every case the question is identical: does the expected return beat the rate I would otherwise earn or pay on that money?

The most important habit the framework instills is recognizing that the answer is conditional on rates. The same investment is a yes in a low-rate world and a no in a high-rate world, and nothing about the investment itself has to change for that flip to happen. When you hear that higher interest rates are "slowing the economy," this is the machinery underneath: millions of projects, large and small, quietly failing to clear a hurdle that just got higher. Run your own numbers against the real rate you face - not the rate you wish existed - and you will make the call the same way a disciplined firm does.