I just reviewed something that many investors overlook: the critical difference between NPV and IRR. These two indicators can give you completely opposite results, and that’s where most make mistakes when evaluating projects.

Let’s start with NPV. It’s basically the present value of all the future cash flows you expect to receive, minus what you invest today. If the result is positive, the investment generates profits. But here’s the important part: what happens if the NPV is negative? It means that the present value of your future flows doesn’t cover your initial investment. In simple terms, you would lose money.

I’ll give you a real example. Imagine you invest $5,000 in a certificate of deposit that will pay you $6,000 in three years, with an interest rate of 8%. When you calculate the present value of those $6,000, you get approximately $4,774. Now subtract your initial investment: $4,774 minus $5,000 equals -$225. That negative NPV is telling you that this financial product isn’t profitable for you at that discount rate.

IRR works differently. It’s the rate of return that equates your initial investment with the future cash flows. It’s expressed as a percentage and compared to a reference rate. If your IRR is higher than that reference rate, the project is profitable.

Now, the problem you see in practice: a project can have a high NPV but a low IRR, or vice versa. This happens because they calculate different things. NPV gives you an absolute number in money. IRR gives you a relative percentage. When this occurs, you need to dig deeper.

Often, the contradiction comes from the discount rate you chose. If you use a very high rate in the NPV calculation, it can turn negative while the IRR remains positive. Especially with volatile cash flows. This is where you need to review your assumptions: does that discount rate truly reflect the project’s risk?

What if the NPV is negative but the IRR seems attractive? Then you’re probably being too optimistic with your future cash flow projections or underestimating the risk. A negative NPV is a red flag you shouldn’t ignore.

The reality is that both metrics have limitations. NPV depends on subjective estimates and doesn’t consider the flexibility to change strategy during the project. IRR assumes you will reinvest the positive flows at the same rate, which rarely happens. Also, if you have unconventional cash flows, IRR can give you multiple results or none at all.

What I’ve learned is that you should use both together. NPV tells you if you will generate real value in money. IRR tells you how efficient that project is in percentage terms. Complement this with ROI, payback period, and profitability index for a complete view.

My recommendation: when evaluating a project, calculate both indicators. If they agree that it’s a good investment, go ahead. If they contradict each other, don’t make a quick decision. Review the discount rates, cash flow projections, project size, expected inflation. Also consider your personal goals, how much risk you can tolerate, and how this fits into your portfolio.

What if the NPV is negative, for example? That’s practically a definitive no. It means that with your current cost of capital, that project destroys value. Unless you have very specific reasons to believe your projections are wrong, it’s better to look for other opportunities.

The investment decision should never be based on a single metric. NPV and IRR are powerful tools, but they are estimates based on assumptions that may not hold. Do your detailed analysis, question your assumptions, and make informed decisions.