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What is IRR and how do you calculate it?

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Last editedJune 20203 min read

The ability to evaluate the profitability of your investments can play an important role in your company’s long-term planning. Many businesses and investors utilise IRR to measure return on potential investments, allowing you to compare and rank different projects based on their projected yield. Find out everything you need to know about the IRR formula – including how to calculate IRR – with our simple guide. First off, what is IRR?

IRR meaning

IRR stands for internal rate of return. It measures your rate of return on a project or investment while excluding external factors. It can be used to estimate the profitability of investments, similar to accounting rate of return (ARR). Generally, a high IRR is preferable to a low IRR, as it signals that a potential project or investment is likely to add value to your business. If you’re using IRR to rank prospective projects, the investment with the highest IRR is probably the one that should be undertaken first (assuming the cost of investment for each project is equal).

How to calculate IRR

Understanding how to calculate IRR can be a challenge, as the IRR formula is a little more complex than many other financial metrics. Here’s the IRR formula you can use in your calculations:

0 = NPV = tt=1 Ct/​(1+IRR)t​​ − C0​


  • Ct = Net cash inflow during period t

  • C0 = Initial investment cost

  • IRR = Internal rate of return

  • t = Number of time periods

That may look a little complex, so let’s break it down. As you can see, the IRR formula equates the net present value (NPV) of future cash flows to zero. In other words, if you calculate the NPV from a potential project and use IRR as the discount rate, subtracting out the original investment, the NPV of the project would equate to zero.

While you can learn how to calculate IRR by hand, it’s important to note that it’s a complex method based on trial and error. This is because you’re trying to work out the rate that makes the NPV equal zero. You may be better served by using Microsoft Excel or other types of business software to complete your calculations.

How to use IRR

The IRR method is often used by businesses to determine which project or investment is worth funding. For example, if you’re trying to work out whether to purchase a new piece of equipment or invest in a new product line, IRR can help you understand the option that’s most likely to yield a healthy rate of return. Although the actual rate of return is likely to differ significantly from the estimated IRR, projects which have a much higher IRR than competing options are likely to offer better value.

There are several different scenarios where the IRR method is particularly useful. If you’re comparing the profitability of expanding existing operations with establishing new operations, your company could use the IRR calculation formula to decide which is the more profitable option. Furthermore, IRR can be helpful for companies considering a stock buyback program; if the company’s stock has a lower IRR than other potential projects, a stock buyback may not be the best idea.

Limitations of IRR

Although IRR can be an excellent tool for estimating the profitability of future projects or investments, it can be a little misleading if you use it on its own.

Projects with a low IRR may have high NPV, indicating that although the rate of return may be slower than other projects, the investment itself is likely to yield significant value for your business. By the same token, IRR may not be the best tool for evaluating projects of different lengths.

Furthermore, IRR assumes that the positive cash flows associated with an investment will be reinvested at the project’s rate of return. This may not be the case, and as a result, the IRR method may not be the most accurate reflection of a project’s cost and profitability. 

Overall, the IRR calculation formula is a valuable metric, but it’s important not to place too much weight on it when making your final decision. There’s another formula called the modified internal rate of return (MIRR) that corrects these issues and may be worth investigating if you’re considering using the IRR formula to evaluate projects.

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