Yes, the internal rate of return does assume reinvestment, and the assumption is built into the formula itself. When you solve for IRR, the math treats every interim cash flow as if it were reinvested at the IRR for the remaining life of the project. A project showing a 25% IRR quietly assumes that every dividend, distribution, or payout received along the way also earns 25% until the final period. That assumption is rarely realistic, and understanding why it exists is the first step toward reading IRR figures with appropriate skepticism.
Why the Formula Implies Reinvestment at the IRR
IRR is defined as the discount rate that makes a project’s net present value equal zero. The formula takes each future cash flow, discounts it back to today at a single rate, and finds the rate where the sum of all those discounted values exactly offsets the initial investment. Because every cash flow is discounted at the same rate, the math works in reverse too: it implies every dollar received before the end of the project compounds forward at that same rate until the final period.
This isn’t a deliberate modeling choice anyone makes. It’s a mechanical consequence of solving for one rate across multiple time periods. The formula has no separate input for what you actually do with the money between cash flows. It simply assumes you keep earning the project’s own return on every dollar, every year, until the end.
A Simple Example Shows the Gap
Suppose you invest $200 and receive $150 in year one, $200 in year two, and $130 in year three. Solving for the rate that drives net present value to zero gives an IRR of about 61.7%. To confirm the formula truly assumes reinvestment at that rate, compound each interim cash flow forward to year three: the $150 grows to roughly $392 after two more years at 61.7%, the $200 grows to about $323 after one year, and the $130 arrives at the end. The total future value comes to approximately $846, which is exactly what $200 compounded at 61.7% for three years produces.
Now consider what happens if you simply hold those interim payments in cash with no reinvestment. Your year-three total drops to $480 ($150 + $200 + $130), a compound annual growth rate of roughly 34%. That’s a staggering gap: 61.7% versus 34%, from the same set of cash flows, depending entirely on what happens to money between payouts. The IRR figure looks impressive on paper, but it assumes you can find equally high-returning opportunities for every dollar the project kicks off along the way.
Modified Internal Rate of Return
The Modified Internal Rate of Return exists specifically to address this flaw. Instead of letting the formula assume reinvestment at the project’s own rate, MIRR asks you to choose two separate rates: a finance rate reflecting your cost of capital, and a reinvestment rate reflecting what you can realistically earn on interim cash flows.
The calculation compounds all positive cash flows forward to the end of the project at your chosen reinvestment rate, creating a single terminal value. It then discounts all negative cash flows back to the present at the finance rate. MIRR is the rate that equates that present value of costs to the terminal value of gains over the project’s life. Because you’re plugging in a realistic reinvestment rate rather than letting the math assume one, the result tends to be more conservative and more honest.
A common choice for the reinvestment rate is the 10-year Treasury yield, which sat near 4.09% as of early March 2026. Using a benchmark like that forces a useful question: if you can only park interim cash flows at around 4%, does this project still look attractive? The answer often differs sharply from what the raw IRR suggests.
When IRR and NPV Rank Projects Differently
Net present value discounts future cash flows at a rate you choose, usually your cost of capital or a required minimum return. That discount rate is typically far lower than a high-performing project’s IRR, which means NPV carries a more conservative reinvestment assumption. When you compare two mutually exclusive projects, the difference can produce opposite recommendations.
Imagine Project A has an IRR of 30% and an NPV of $50,000, while Project B has an IRR of 20% and an NPV of $80,000. Ranked by IRR, Project A wins. But Project B creates more total wealth. The conflict usually arises when projects differ in size, duration, or the timing of their cash flows. IRR measures percentage growth of the capital involved, which favors smaller or shorter projects that return money quickly. NPV measures the absolute dollar increase in value, which is what actually shows up in your account.
For most investors choosing between competing opportunities, NPV is the more reliable tiebreaker. It tells you how much richer you’ll actually be, rather than how impressive the percentage looks.
Why the Assumption Hurts Most in Real Estate
Real estate is where the reinvestment assumption bites hardest, because commercial properties routinely distribute cash to investors over long holding periods. A multifamily deal structured to return capital through quarterly or annual distributions will show a higher IRR than the investor is likely to achieve in practice, unless those distributions can be redeployed into equally high-returning projects every single time.
Experienced real estate investors rarely look at IRR in isolation. The equity multiple, which divides total distributions by total invested capital, gives a simpler picture of how much money you actually got back relative to what you put in. It ignores the time value of money, so it won’t tell you anything about efficiency or speed. But it also won’t mislead you about reinvestment. A deal with a 2.0x equity multiple doubled your money, regardless of what happened to distributions between receipt and final accounting.
Using IRR and equity multiple together gives a fuller picture. A short-hold deal with a high IRR but low equity multiple might look great on a percentage basis while delivering modest total returns. A longer-hold deal with a lower IRR but high equity multiple might put more money in your pocket.
XIRR Fixes Timing but Keeps the Assumption
The standard IRR formula assumes cash flows arrive at perfectly regular intervals, like once per year or once per quarter. Real investments rarely cooperate. Capital calls in a private equity fund, irregular dividend payments, or a lump-sum exit that closes mid-quarter all violate this assumption. Forcing irregular cash flows into a standard IRR calculation produces a number that doesn’t reflect actual timing.
XIRR solves that by assigning a specific date to each cash flow and discounting based on the exact number of days between transactions. The result is an annualized rate of return that accounts for real-world timing. In spreadsheet software, the XIRR function requires both a list of cash flow amounts and a corresponding list of dates.
The reinvestment assumption still exists in XIRR. Interim cash flows are still implicitly treated as though they earn the solved rate for the remainder of the investment. The timing component is accurate, which prevents the additional distortion that comes from pretending irregular cash flows are evenly spaced, but the underlying reinvestment issue doesn’t disappear. For most investors working with real portfolio data, XIRR is the more appropriate starting point before layering on adjustments like MIRR.