Finance

NPV vs IRR: How to Evaluate Any Investment Like a CFO

Net present value (NPV) and internal rate of return (IRR) are the two standard ways to decide whether an investment is worth making. They use the same cash-flow forecast and usually agree. When they disagree, knowing why will stop you from choosing the wrong project.

The idea behind both: money has a time value

A dollar today is worth more than a dollar in three years, because today’s dollar could be invested in the meantime and because the future is uncertain. Both NPV and IRR convert future cash flows into today’s terms. They just express the answer differently.

NPV: how much value does the project add?

NPV = Σ cash flowt ÷ (1 + r)t, where r is your discount rate — the return you require, often your cost of capital.

Example: equipment costs $100,000 and saves $30,000, $35,000, $40,000 and $45,000 over four years. At a 10% discount rate, NPV ≈ +$16,987. Positive NPV means the project earns more than 10% and adds about $17,000 of value in today’s dollars.

Decision rule: accept if NPV > 0. Calculate yours with the NPV calculator.

IRR: what return does the project earn?

IRR is the discount rate that makes NPV exactly zero. For the same equipment project, IRR ≈ 17.1%.

Decision rule: accept if IRR > your required return. 17.1% beats 10%, so — like NPV — IRR says yes. Try it with the IRR calculator.

IRR’s appeal is that it is a single percentage that is easy to compare with a loan rate, a hurdle rate or stock-market returns.

When NPV and IRR disagree

For a single yes/no decision on a normal project (one upfront cost followed by positive cash flows), NPV and IRR always agree. Conflicts appear when you have to choose between projects.

Scale

Two mutually exclusive options, 10% discount rate:

IRR prefers A; NPV prefers B. If you can only do one and capital is available, B adds more than twice as much value even though its percentage return is lower. A high return on a small amount can be worth less than a decent return on a large amount.

Timing

Projects that return cash late can show a lower IRR than projects that return cash early, even if they create more value. IRR implicitly assumes interim cash flows are reinvested at the IRR itself, which is often unrealistic for high-IRR projects.

Unusual cash flows

If cash flows switch from negative to positive more than once — for example a mine with a large clean-up cost at the end — there can be more than one IRR, or none. NPV still gives one clear answer.

Which should you rely on?

Corporate finance textbooks generally favor NPV for choosing between projects because it measures value in dollars and handles scale, timing and unusual cash flows correctly. In practice, use both:

Choosing the discount rate

NPV is only as good as the discount rate. Businesses typically use their weighted average cost of capital (WACC), adding a premium for riskier projects. Individuals can use the return they could reasonably earn elsewhere at similar risk. Always test a higher rate: a project that only works at a low discount rate is fragile.

Common mistakes

Key takeaways