Economics
Internal Rate of Return (IRR)
Quick fact
The IRR is the discount rate at which the Net Present Value of all cash flows equals zero. For a simple investment of $100 today returning $110 next year, the IRR is 10%—exactly the return you earned.
Why this is interesting
You invest in a project today, expecting returns over the next few years. But how do you decide if it's truly a good deal? The Internal Rate of Return (IRR) gives you a single number—the average annual return—that instantly tells you whether you are beating the market or your cost of borrowing.
Read the full explanation
Understanding Internal Rate of Return (IRR)
Imagine a seesaw: on one side is the money you put in (the initial investment), on the other side are all the future cash flows you get back. The IRR is the balancing point—the interest rate that makes both sides equal in today’s money. Suppose you invest $1,000 in a business that will pay you $300 each year for 4 years. The IRR is the rate that discounts those four $300 payments back to a present value of exactly $1,000. If that rate is 12%, it means the project effectively earns 12% per year. Compare it to your cost of borrowing: if you can borrow at 8%, the project is attractive; if you need to borrow at 15%, it’s not. The IRR is like a speedometer for your investment’s earning power.
A deeper explanation
Mechanically, IRR solves for r in the equation: Initial Investment = Σ (Cash Flowt / (1+r)^t). This polynomial equation may have multiple solutions if cash flows change sign more than once (e.g., investment then later additional costs). The IRR rule—accept projects where IRR cost of capital—assumes that intermediate cash flows can be reinvested at the same IRR, which is often unrealistic. Despite this limitation, IRR remains popular because it expresses return as an intuitive percentage, unlike NPV which gives a dollar amount. It is widely used in capital budgeting, private equity, and project finance to rank mutually exclusive projects. Understanding IRR deepens your grasp of how time value of money, risk, and reinvestment assumptions shape investment real-world decisions.