Discount Rates and Long-Term Infrastructure: Why Interest Rates Matter

Explaining how the discount rate, influenced by interest rates, shapes the financial viability of long-term infrastructure projects.

By Garret Merkley · Explainer · Jun 17, 2026

Branched from Understanding Value for Money in Infrastructure Projects

Quick take

A discount rate converts future costs and benefits of a project into today's value.
It reflects the time value of money and the risk involved in waiting for future returns.
Higher interest rates generally lead to higher discount rates, making future benefits seem less valuable today.
This significantly impacts which long-term infrastructure projects appear financially viable and attractive for investment.

A discount rate is a financial tool used to convert future cash flows—both costs and benefits—into their equivalent value today. For long-term infrastructure projects, which involve expenses and returns stretching over decades, it's essential for comparing money received or spent at different points in time. The prevailing interest rates in the broader economy are a significant factor in determining this rate, making them central to project evaluation.

How It Works: The Time Value of Money

At its core, the discount rate reflects the "time value of money"—the idea that a dollar today is worth more than a dollar received a year from now. This is due to several factors: inflation erodes purchasing power, there's an opportunity cost (money could be invested elsewhere to earn a return), and there's inherent risk that future payments might not materialize. The discount rate accounts for these elements, effectively "discounting" future values back to the present.

How It Works: Valuing Long-Term Projects

When evaluating an infrastructure project like a new bridge, power plant, or high-speed rail line, analysts project all its future construction costs, maintenance expenses, and revenue streams (e.g., tolls, energy sales) over its lifespan. The discount rate is then applied to each of these future amounts. By doing so, every future dollar is adjusted to its present-day equivalent, allowing for a fair comparison of the project's total costs versus its total benefits, expressed as a Net Present Value (NPV).

How It Works: The Interest Rate Connection

The general interest rate environment plays a critical role in setting the discount rate. If interest rates are high, the opportunity cost of capital is also high—investors could easily earn a good return by simply putting their money into bonds or savings accounts. Therefore, for an infrastructure project to be attractive, it must promise an even higher return, leading to a higher discount rate being applied to its future cash flows. Conversely, low interest rates typically lead to lower discount rates, making future returns look more valuable today.

The chosen discount rate profoundly impacts which long-term infrastructure projects are deemed financially viable. A small change in the discount rate can shift a project's Net Present Value from positive to negative, effectively determining whether it gets built. For projects with very long lifespans (50-100+ years), future costs and benefits are heavily discounted, meaning only the earliest returns or most substantial long-term benefits might still appear significant. This makes the discount rate a crucial lever in public policy, private investment decisions, and the allocation of resources towards foundational societal assets.

Is the discount rate always the same for all projects?

No, the discount rate can vary significantly. It depends on factors like the project's specific risk profile, the cost of capital for the entity undertaking the project (e.g., government vs. private company), and the general economic conditions at the time of evaluation.

Who sets the discount rate for public infrastructure projects?

For public projects, government agencies typically set guidelines or specific rates. These are often based on government borrowing costs, societal risk premiums, and policy objectives, sometimes adjusting for specific project risks or social benefits.

How does inflation factor into the discount rate?

The discount rate typically accounts for inflation, either directly by using a "nominal" discount rate that includes expected inflation, or indirectly by using a "real" discount rate applied to inflation-adjusted (real) cash flows. Consistency in approach is key.

Can a discount rate be too low?

Yes. A discount rate that is too low might make a project appear more attractive than it truly is, overstating the present value of future benefits and potentially leading to investments in projects that don't offer sufficient returns given their risk and opportunity costs.

What's the difference between a discount rate and an interest rate?

An interest rate is typically the cost of borrowing money or the return on an investment. A discount rate *uses* interest rates as a component but also incorporates other factors like risk premium and opportunity cost to determine the rate at which future cash flows are reduced to their present value.