NPV and IRR Explained: How to Tell Whether a Project or Investment Is Worth It

Why "Total Profit" Is Not Enough

That project pays back $18,000 on a $10,000 investment, a profit of $8,000. But when the money arrives matters, because a dollar today is worth more than a dollar in four years: you can invest it, and inflation eats away at the later dollar. Two projects with the same total profit can be very different if one pays early and the other late.

NPV and IRR solve this by taking the timing of each cash flow into account.

👉 Evaluate your own project with our free NPV and IRR calculator →

Net Present Value (NPV)

NPV adds up all future cash flows, discounts each one back to today, and subtracts the initial investment:

NPV = Σ cash flow in year t ÷ (1 + r)^t − initial investment

Here r is the discount rate, the return you require or could earn elsewhere with similar risk. For the example at 10%:

Swipe sideways to see all columns. The $18,000 of future cash is worth only $13,887.71 in today's money, so after the $10,000 investment the project adds $3,887.71 of value. The rule is simple: NPV above zero, accept; below zero, reject.

Internal Rate of Return (IRR)

The IRR is the discount rate at which the NPV becomes exactly zero. Put differently, it is the project's own yearly return, taking timing into account. In the example it is 24.89%. Compare it with your required return: IRR above the required return means the project is worth doing.

You can see it in the NPV at different discount rates:

The higher the rate you demand, the lower the NPV, and it crosses zero at about 25%, which is the IRR. If you could earn 30% elsewhere, this project would not be worth it.

Other Measures You Will See

• Profitability index = present value of future cash flows ÷ investment. Here $13,887.71 ÷ $10,000 = 1.39 at 10%: every dollar invested returns $1.39 in today's money. Above 1 is good.
• Payback period = how long it takes to recover the investment without discounting: 2.6 years in the example.
• Discounted payback = the same, using discounted cash flows: 3.1 years at 10%. It is always longer.

Payback is easy to understand, but it ignores everything after the payback date, so use it as a rough check on risk, not as the main decision tool.

Timing Changes the Answer

Both of these projects pay back $18,000 in total on a $10,000 investment:

Project B returns the same total, but gets the money back sooner, so it is worth about $610 more in today's dollars and has a much higher IRR. The total hides the difference.

And size matters too. If the same cash flows required a $20,000 investment, the NPV at 10% would be −$6,112.29 and the IRR negative: the project would destroy value.

How to Use NPV and IRR Step by Step

1. Estimate the cash flows of the project for each year, as honestly as you can, including costs and taxes.
2. Choose a discount rate that reflects the return you could get elsewhere with similar risk, or your cost of borrowing.
3. Compute the NPV. Positive means the project beats your required return.
4. Check the IRR and compare it with the same rate.
5. Test the assumptions. Lower the cash flows by 20%, delay them a year or raise the discount rate, and see if the decision changes.
6. Compare with simpler measures. A project with a good NPV but a very long payback is riskier.

For a single investment where all the cash comes at the end, our guide on ROI and annualized return is simpler.

Common Pitfalls

• Overly optimistic cash flows. The result is only as good as the forecast. Test a downside case.
• The wrong discount rate. A too-low rate makes almost anything look good.
• IRR with unusual cash flows. When cash flows change sign more than once, there can be more than one IRR, or none. Use NPV in that case.
• Choosing between projects by IRR alone. A small project can have a high IRR but add less total value than a larger one. When projects exclude each other, prefer the higher NPV.
• Forgetting the end. Include resale value, working capital recovery or cleanup costs at the end of the project.
• Ignoring inflation and risk. Make sure cash flows and the discount rate are both in nominal terms or both in real terms.

Frequently Asked Questions

What is a good NPV?

Any NPV above zero means the project earns more than your required return. A larger NPV adds more value, but compare it with the size of the investment.

What is a good IRR?

One that is higher than the return you require or could get elsewhere with the same risk. If your cost of capital is 10%, an IRR of 24.9% is attractive, though you should test the cash flow assumptions.

How do I choose the discount rate?

Use the return you could earn on an alternative with similar risk, your cost of borrowing, or the target return of your business. Test a few rates, as in the table above.

What is the difference between NPV and IRR?

NPV gives the value added in dollars at a chosen rate. IRR gives the project's own return as a percentage. They usually agree on whether to accept a project, but NPV is better for comparing projects of different sizes.

Can I use NPV for a personal decision?

Yes. For example, to compare paying more for an energy-efficient appliance with the savings it brings each year, or paying for a course with the extra income you expect.

Conclusion & Recommended Next Steps

NPV and IRR turn a list of future cash flows into a decision. Estimate the money in and out year by year, choose a realistic discount rate and see whether the NPV is above zero and the IRR above your required return, then test what happens if the cash arrives later or smaller. Enter your own numbers in the calculator and compare scenarios.

Disclaimer: This guide is intended solely for educational and informational purposes and does not constitute personalized financial, investment, legal, or tax advice. NPV and IRR depend on forecasts that may prove wrong, and the figures above are illustrations based on the stated assumptions. Consult a qualified financial professional before you make an investment decision.