NPV vs IRR: Differences, Formulas, and When to Use Each
What Is NPV?
Net present value sums the present values of all cash inflows and outflows associated with a project. If NPV is positive, the project creates value above the required return. If negative, it destroys value. NPV is the gold standard of capital budgeting because it directly measures wealth creation in dollar terms.
What Is IRR?
The internal rate of return is the discount rate at which NPV equals zero. Think of it as the annualized return the project generates on invested capital. If the IRR exceeds your cost of capital, the project is worth pursuing — at least by this metric alone.
NPV vs IRR: Side-by-Side Comparison
| Dimension | NPV | IRR |
|---|---|---|
| Output | Dollar amount (value created) | Percentage return |
| Decision rule | Accept if NPV > 0 | Accept if IRR > cost of capital |
| Reinvestment assumption | Reinvests at the discount rate (WACC) | Reinvests at the IRR itself |
| Mutually exclusive projects | Correctly ranks projects by value | Can give misleading rankings |
| Multiple solutions | Always gives one answer | Can produce multiple IRRs with non-conventional cash flows |
| Scale sensitivity | Captures project size (dollar value) | Ignores scale (percentage only) |
| Ease of communication | Less intuitive for non-finance audiences | Easy to explain (“this project earns 18%”) |
| Preferred by academics | Yes — theoretically superior | No — known limitations |
| Preferred by practitioners | Used alongside IRR | Widely used in PE and project finance |
| Handles different discount rates | Can use varying rates per period | Assumes single rate across all periods |
The Reinvestment Rate Problem
This is the critical difference most people miss. NPV assumes intermediate cash flows are reinvested at the discount rate (usually WACC), which is realistic. IRR assumes reinvestment at the IRR itself — which is often unrealistically high. For a project with a 30% IRR, the model assumes you can reinvest every interim cash flow at 30%. That’s almost never true.
This is why NPV and IRR can rank mutually exclusive projects differently. A smaller project with a higher IRR might look better by IRR, but a larger project with a lower IRR could create far more total value (higher NPV).
When NPV and IRR Conflict
For independent projects (accept/reject decisions), NPV and IRR always agree — if IRR > WACC, then NPV > 0. The conflict arises when comparing mutually exclusive projects that differ in scale, timing, or duration. In those cases, always go with NPV. It correctly accounts for project size and uses a more realistic reinvestment assumption.
Key Takeaways
- NPV measures dollar value created; IRR measures percentage return — both are useful but answer different questions
- NPV is theoretically superior because it uses a realistic reinvestment assumption (WACC vs IRR)
- For independent projects, NPV and IRR always give the same accept/reject decision
- For mutually exclusive projects, trust NPV — IRR can mislead when projects differ in scale or timing
- IRR can produce multiple solutions with unconventional cash flows; NPV always gives one clear answer
Frequently Asked Questions
Which is better, NPV or IRR?
NPV is theoretically superior and should be the primary decision tool. However, IRR is widely used because a percentage return is intuitive and easy to communicate. Best practice is to use both: NPV for the final investment decision, IRR for quick screening and communication with stakeholders.
Can IRR give you multiple answers?
Yes. When cash flows switch signs more than once (e.g., initial outflow, inflows, then another outflow), the IRR equation can have multiple solutions. This is called the “multiple IRR problem.” NPV doesn’t have this issue — it always gives a single, unambiguous result.
Why do private equity firms prefer IRR?
Private equity firms use IRR because their business model revolves around earning returns on invested capital over defined holding periods. LPs evaluate fund performance by IRR. However, sophisticated PE firms also track MOIC (multiple on invested capital) and DPI to capture what IRR misses — particularly timing manipulation.
What discount rate should I use for NPV?
Typically the weighted average cost of capital (WACC) for corporate projects, or the investor’s required rate of return for personal investments. The rate should reflect the risk of the specific cash flows being discounted.
What is a good IRR?
It depends entirely on context. For corporate projects, any IRR above the company’s WACC (often 8–12%) creates value. For private equity, target IRRs are typically 20–25%. For venture capital, expected IRRs are 30%+ given the higher risk.