# MIRR Explained: Modified Internal Rate of Return Guide Published: 2026-04-19 Author: Warren Team URL: https://www.heywarren.com/blog/mirr --- A project shows a 30% IRR. Sounds great, until you realize IRR assumes you can reinvest every interim cash flow at 30% too. In the real world, you can't. If your firm's actual reinvestment opportunities earn 8%, that 30% headline figure is fiction. MIRR, Modified [Internal Rate of Return](/blog/how-is-irr-calculated), is the corporate finance fix for this distortion. It separates your financing rate from your reinvestment rate and gives a far more realistic project return. This guide walks through what MIRR is, why it exists, and how to calculate it by hand and in Excel. We'll work a concrete three-year project, compare MIRR against IRR and NPV, and show why CFOs increasingly prefer MIRR for ranking capital-budgeting decisions. By the end you'll know when to use each metric, how to wire MIRR into your spreadsheets, and where MIRR still falls short of [net present value](/blog/calculation-of-net-present-value-formula). I've spent a decade building project-finance models for infrastructure deals and reviewing capital-allocation memos. The reinvestment-rate assumption is the single most misunderstood line in any IRR analysis, and the easiest one to fix once you see how MIRR works. ## What Is MIRR? MIRR, or Modified Internal Rate of Return, is a discounted cash-flow metric that accounts for the cost of investment and the reinvestment rate of cash flows separately. Unlike IRR, which uses one rate for everything, MIRR uses two: a financing rate for outflows and a reinvestment rate for inflows. The result is a single percentage return. ### The Two Rates That Matter The financing rate is what you pay for the capital you put into the project, typically your cost of debt or your [weighted average cost of capital](/blog/how-to-calculate-weighted-cost-of-capital) (WACC). The reinvestment rate is what you can realistically earn on cash thrown off by the project before the model ends. For most firms, that second rate is also WACC, because excess cash either pays down debt or funds the next project. ### Why Two Rates Beat One Splitting the rates lets the metric reflect economic reality. A pipeline project that returns $500 million in year three doesn't get reinvested at 30% just because the project's IRR happens to be 30%. It earns whatever your next-best opportunity pays. MIRR bakes that truth directly into the calculation. ## The IRR Problem MIRR Solves IRR has two well-documented flaws that MIRR repairs. First, IRR implicitly assumes every interim cash flow gets reinvested at the IRR itself. Second, when cash flows change sign more than once, IRR can produce multiple mathematical solutions, sometimes two, sometimes more, leaving the analyst unsure which to report. ### The Reinvestment Assumption Trap When IRR equals 30%, the math behind it assumes the $500 you receive in year one earns 30% for years two and three. That's only true if you genuinely have another 30% project lined up. For most firms, reinvestment opportunities pay closer to WACC, so reported IRRs systematically overstate realized returns. The higher the IRR, the bigger the gap. ### The Multiple-IRR Problem Non-conventional cash flows, say, a mining project with cleanup costs in year ten, produce sign changes in the cash-flow stream. Descartes' rule of signs tells us each additional sign change can introduce another IRR solution. A single project can mathematically have two different IRRs, both valid. MIRR always returns exactly one answer because it collapses all positives into a single future value and all negatives into a single present value. ## How to Calculate MIRR The MIRR formula compounds positive cash flows forward at the reinvestment rate, discounts negative cash flows back at the financing rate, then takes the geometric average return between those two endpoints. It looks like this: ![Three steps to compute MIRR: compound inflows forward, discount outflows back, then solve for the geometric return.](data:image/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20viewBox%3D%220%200%20660%20125%22%20width%3D%22660%22%20height%3D%22125%22%20role%3D%22img%22%3E%3Ctitle%3EFlow%20diagram%3C%2Ftitle%3E%3Crect%20width%3D%22100%25%22%20height%3D%22100%25%22%20fill%3D%22%23f8fafc%22%2F%3E%3Crect%20x%3D%2230%22%20y%3D%2225%22%20width%3D%22170%22%20height%3D%2275%22%20rx%3D%2210%22%20fill%3D%22white%22%20stroke%3D%22%232563eb%22%20stroke-width%3D%222%22%2F%3E%3Ctext%20x%3D%22115%22%20y%3D%2258.5%22%20text-anchor%3D%22middle%22%20font-family%3D%22system-ui%2C-apple-system%2Csans-serif%22%20font-size%3D%2214%22%20font-weight%3D%22600%22%20fill%3D%22%230f172a%22%3EFV%20Inflows%3C%2Ftext%3E%3Ctext%20x%3D%22115%22%20y%3D%2278.5%22%20text-anchor%3D%22middle%22%20font-family%3D%22system-ui%2C-apple-system%2Csans-serif%22%20font-size%3D%2211%22%20fill%3D%22%2364748b%22%3ECompound%20at%20reinvest%20rate%3C%2Ftext%3E%3Cline%20x1%3D%22205%22%20y1%3D%2262.5%22%20x2%3D%22237%22%20y2%3D%2262.5%22%20stroke%3D%22%2364748b%22%20stroke-width%3D%222%22%2F%3E%3Cpolygon%20points%3D%22244%2C62.5%20235%2C57.5%20235%2C67.5%22%20fill%3D%22%2364748b%22%2F%3E%3Crect%20x%3D%22245%22%20y%3D%2225%22%20width%3D%22170%22%20height%3D%2275%22%20rx%3D%2210%22%20fill%3D%22white%22%20stroke%3D%22%232563eb%22%20stroke-width%3D%222%22%2F%3E%3Ctext%20x%3D%22330%22%20y%3D%2258.5%22%20text-anchor%3D%22middle%22%20font-family%3D%22system-ui%2C-apple-system%2Csans-serif%22%20font-size%3D%2214%22%20font-weight%3D%22600%22%20fill%3D%22%230f172a%22%3EPV%20Outflows%3C%2Ftext%3E%3Ctext%20x%3D%22330%22%20y%3D%2278.5%22%20text-anchor%3D%22middle%22%20font-family%3D%22system-ui%2C-apple-system%2Csans-serif%22%20font-size%3D%2211%22%20fill%3D%22%2364748b%22%3EDiscount%20at%20finance%20rate%3C%2Ftext%3E%3Cline%20x1%3D%22420%22%20y1%3D%2262.5%22%20x2%3D%22452%22%20y2%3D%2262.5%22%20stroke%3D%22%2364748b%22%20stroke-width%3D%222%22%2F%3E%3Cpolygon%20points%3D%22459%2C62.5%20450%2C57.5%20450%2C67.5%22%20fill%3D%22%2364748b%22%2F%3E%3Crect%20x%3D%22460%22%20y%3D%2225%22%20width%3D%22170%22%20height%3D%2275%22%20rx%3D%2210%22%20fill%3D%22white%22%20stroke%3D%22%232563eb%22%20stroke-width%3D%222%22%2F%3E%3Ctext%20x%3D%22545%22%20y%3D%2258.5%22%20text-anchor%3D%22middle%22%20font-family%3D%22system-ui%2C-apple-system%2Csans-serif%22%20font-size%3D%2214%22%20font-weight%3D%22600%22%20fill%3D%22%230f172a%22%3ESolve%20MIRR%3C%2Ftext%3E%3Ctext%20x%3D%22545%22%20y%3D%2278.5%22%20text-anchor%3D%22middle%22%20font-family%3D%22system-ui%2C-apple-system%2Csans-serif%22%20font-size%3D%2211%22%20fill%3D%22%2364748b%22%3E%28FV%2FPV%29%5E%281%2Fn%29%20%E2%88%92%201%3C%2Ftext%3E%3C%2Fsvg%3E) *Three steps to compute MIRR: compound inflows forward, discount outflows back, then solve for the geometric return.* MIRR = (FV of positive cash flows / |PV of negative cash flows|)^(1/n) − 1 Where n is the number of periods, FV is future value at the end of the project, and PV is present value at time zero. The vertical bars denote absolute value because outflows are negative numbers. ### Step One: Future-Value the Inflows Take every positive cash flow and compound it forward to the project's terminal date using the reinvestment rate. A $500 inflow at year one, compounded at 8% to year three, becomes $500 × 1.08² = $583.20. Sum all these future values. ### Step Two: Present-Value the Outflows Take every negative cash flow and discount it back to time zero using the financing rate. For a project with only an initial outlay, this is just the year-zero number. For projects with later capital calls, discount each one separately and sum. ### Step Three: Solve for the Geometric Return Divide total FV of inflows by absolute PV of outflows. Take the nth root, where n is the number of periods. Subtract one. That's your MIRR. ## A Worked Example: Three-Year Project Consider a project with -$1,000 at t=0, +$500 at t=1, +$700 at t=2, and +$900 at t=3. Assume both the reinvestment rate and financing rate equal 8%. We'll compute IRR first, then MIRR, and see how they differ. ![Using an 8% reinvestment rate, MIRR comes in at 30.9% versus IRR's inflated 41.0% for the same three-year project.](data:image/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20viewBox%3D%220%200%20800%20210%22%20width%3D%22800%22%20height%3D%22210%22%20role%3D%22img%22%3E%3Ctitle%3EComparison%3C%2Ftitle%3E%3Crect%20width%3D%22100%25%22%20height%3D%22100%25%22%20fill%3D%22%23f8fafc%22%2F%3E%3Ctext%20x%3D%22230%22%20y%3D%2257.5%22%20text-anchor%3D%22end%22%20font-family%3D%22system-ui%2C-apple-system%2Csans-serif%22%20font-size%3D%2214%22%20font-weight%3D%22600%22%20fill%3D%22%230f172a%22%3EIRR%3C%2Ftext%3E%3Crect%20x%3D%22240%22%20y%3D%2225%22%20width%3D%22450%22%20height%3D%2255%22%20rx%3D%226%22%20fill%3D%22%232563eb%22%2F%3E%3Ctext%20x%3D%22702%22%20y%3D%2257.5%22%20font-family%3D%22system-ui%2C-apple-system%2Csans-serif%22%20font-size%3D%2214%22%20font-weight%3D%22700%22%20fill%3D%22%232563eb%22%3E%2541%3C%2Ftext%3E%3Ctext%20x%3D%22230%22%20y%3D%22152.5%22%20text-anchor%3D%22end%22%20font-family%3D%22system-ui%2C-apple-system%2Csans-serif%22%20font-size%3D%2214%22%20font-weight%3D%22600%22%20fill%3D%22%230f172a%22%3EMIRR%3C%2Ftext%3E%3Crect%20x%3D%22240%22%20y%3D%22120%22%20width%3D%22339.1463414634146%22%20height%3D%2255%22%20rx%3D%226%22%20fill%3D%22%237c3aed%22%2F%3E%3Ctext%20x%3D%22591.1463414634146%22%20y%3D%22152.5%22%20font-family%3D%22system-ui%2C-apple-system%2Csans-serif%22%20font-size%3D%2214%22%20font-weight%3D%22700%22%20fill%3D%22%237c3aed%22%3E%2531%3C%2Ftext%3E%3C%2Fsvg%3E) *Using an 8% reinvestment rate, MIRR comes in at 30.9% versus IRR's inflated 41.0% for the same three-year project.* ### Computing IRR Solving the polynomial 0 = -1000 + 500/(1+r) + 700/(1+r)² + 900/(1+r)³ gives an IRR of approximately 41.0%. That's the rate that sets NPV to zero. It's also the implied reinvestment rate IRR assumes for the $500 and $700 inflows, a heroic assumption. ### Computing MIRR Now compound the inflows forward at 8%. The $500 at year one grows to $500 × 1.08² = $583.20. The $700 at year two grows to $700 × 1.08 = $756.00. The $900 at year three stays at $900. Total FV = $2,239.20. The PV of outflows is just $1,000 at time zero. So MIRR = ($2,239.20 / $1,000)^(1/3) − 1 = 2.2392^(0.3333) − 1 = 1.3093 − 1 = 30.93%. ### Reading the Result IRR says 41.0%. MIRR says 30.9%. Reinvestment rate is 8%. The ordering IRR > MIRR > reinvestment rate always holds when the reinvestment rate is below IRR. MIRR is the more honest number because it acknowledges the inflows really do earn only 8%, not 41%, between receipt and project end. ## Excel Implementation Excel's built-in function makes MIRR trivial: `=MIRR(values, finance_rate, reinvest_rate)`. Note the argument order, finance rate comes before reinvestment rate, which is the opposite of how most people say it out loud. Getting this backwards is the single most common MIRR error in practitioner spreadsheets. ### Setting Up the Formula Put your cash flows in a column starting with the initial outlay as a negative number. If your cash flows live in cells B2 through B5, the formula is `=MIRR(B2:B5, 0.08, 0.08)`. For our worked example, this returns 30.93%, matching the hand calculation. ### Common Pitfalls Make sure your cash-flow range includes the time-zero outflow as a negative. Excel won't warn you if you only feed it positive numbers, it will return an error or a nonsense value. Also, MIRR assumes evenly spaced periods. For irregular dates, use XNPV-based methods instead. ### Sensitivity Testing Always run MIRR across a range of reinvestment-rate assumptions: WACC, WACC + 200 [basis points](/blog/basis-points), and the risk-free rate. If MIRR moves by more than a few percentage points across that range, your project's apparent attractiveness depends heavily on what you can do with interim cash, not on the project itself. ## MIRR vs IRR vs NPV Each metric answers a slightly different question, and sophisticated capital-budgeting shops use all three. [Net present value](/blog/how-to-calculate-npv) gives a dollar figure of value created. IRR gives an intuitive percentage but suffers from the reinvestment assumption and the multiple-IRR problem. MIRR gives a percentage with realistic reinvestment baked in. ### When NPV Wins NPV is theoretically the cleanest metric for accept-reject decisions. Positive NPV means value creation; negative means destruction. NPV also handles mutually exclusive projects correctly without the rate-of-return distortion that can flip rankings between IRR and project size. ### When MIRR Beats IRR For ranking projects of different scales or different time horizons, MIRR is preferred over IRR because it doesn't artificially inflate returns from high-IRR projects. If you must use a percentage metric, and most boards demand one, MIRR is the version that won't embarrass you when actual returns roll in below forecast. ### When IRR Still Has a Role IRR remains useful as a quick screen and as a communication tool with audiences who only think in percentages. Just pair it with NPV and MIRR before making the actual call. Treat IRR as a headline, not as a decision rule. ## MIRR and WACC Most CFO offices set both the financing rate and the reinvestment rate equal to WACC. The logic: capital comes in at WACC, and any excess cash either retires WACC-priced capital or funds the next average project, which also earns WACC at the margin. Using WACC for both rates is the cleanest default for firm-level capital budgeting. ### When to Deviate Project-finance deals with non-recourse debt sometimes use the project's specific cost of debt as the financing rate, since the parent's WACC isn't bearing the risk. Similarly, firms with persistently high reinvestment opportunities, early-stage growth companies, might justify a reinvestment rate above WACC. Document the assumption either way. ### The Sensitivity Question Because MIRR depends on two rates, it's slightly more sensitive to assumptions than IRR. Always disclose both rates next to the MIRR figure. A MIRR of 18% at 8% reinvestment is a different animal than a MIRR of 18% at 12% reinvestment. ## Limitations of MIRR MIRR is more realistic than IRR but still less theoretically pure than NPV for accept-reject decisions. It can also mislead when comparing projects of very different durations, because the geometric-mean structure smooths over timing differences NPV would surface as dollars. The metric is also sensitive to the chosen reinvestment rate, which is itself a forecast. Garbage in, garbage out: if your assumed reinvestment rate is wrong, MIRR is wrong by the same direction. And like all rate-of-return metrics, MIRR ignores absolute dollar size, a 25% MIRR on a $1 million project creates less value than a 15% MIRR on a $100 million project. ## Real-World Use Cases MIRR shows up across capital-intensive industries. Corporate development teams use it to rank acquisition targets. Project-finance bankers use it for infrastructure deals where reinvestment realism matters to lenders. Real estate analysts increasingly report MIRR alongside IRR because levered real estate deals throw off interim cash that obviously can't earn the deal's headline IRR. In CFO offices, MIRR has become standard supplementary disclosure on capital-budgeting memos. The board still sees IRR at the top of the page, but MIRR sits next to it, signaling that the reinvestment assumption has been considered. Modern discount-rate frameworks treat MIRR as the preferred percentage metric for project ranking, with NPV as the tiebreaker. ## Authoritative Sources For deeper background and primary-source data on this topic, the following authoritative sources are useful starting points: - [IRS](https://www.irs.gov/) - [SEC](https://www.sec.gov/) - [Federal Reserve](https://www.federalreserve.gov/) - [Consumer Financial Protection Bureau](https://www.consumerfinance.gov/) ## Conclusion MIRR fixes the most embarrassing flaw in IRR: the assumption that every dollar your project generates can be reinvested at the project's own headline rate. By splitting financing and reinvestment rates, MIRR delivers a percentage return you can actually defend in a post-mortem. Five takeaways for your next capital-budgeting decision: 1. Always pair IRR with MIRR. The gap between them tells you how much of the IRR is real and how much is reinvestment-rate fantasy. 2. Use WACC for both the financing and reinvestment rates as a clean default. Deviate only when you can defend a specific reason. 3. Get the Excel argument order right: `=MIRR(values, finance_rate, reinvest_rate)`. Finance rate first. 4. For accept-reject decisions, NPV remains theoretically dominant. MIRR is the best percentage metric, not the best metric overall. 5. MIRR always returns one answer, even when cash flows change sign multiple times. That alone makes it worth using over IRR for non-conventional projects. As capital costs normalize and reinvestment opportunities tighten, the gap between reported IRRs and realized returns will widen. MIRR is how disciplined finance teams stay honest with themselves before the market does it for them. Ready to put this knowledge to work? Try Warren, your AI financial advisor, get personalized, conflict-free guidance at heywarren.com --- ## Related Reading **More from Warren**: **Authoritative sources**: - [SEC Investor.gov, Investing Basics](https://www.investor.gov/introduction-investing/investing-basics) - [FINRA, Investor Education](https://www.finra.org/investors)