IRR vs MIRR: Which Return Measure to Trust
By Devon Coombs, CPA, MBA · Teaching Professor of Finance, Santa Clara University · Reviewed August 2026
Quote IRR when cash flows are conventional and the audience expects the standard percentage return. Use MIRR when interim cash flows are large, the computed IRR is high, or cash flows change sign more than once, because MIRR replaces the assumption that interim cash reinvests at the IRR itself with an explicit, achievable reinvestment rate. MIRR is generally the more honest estimate of the return an investor can actually compound.
| IRR | MIRR | |
|---|---|---|
| Reinvestment assumption | Interim cash flows compound at the IRR itself | Interim cash flows compound at a stated reinvestment rate |
| Uniqueness | Can have multiple or no solutions when signs change more than once | One unique solution |
| Inputs | Cash flows only | Cash flows plus a finance rate and a reinvestment rate |
| Bias at high returns | Tends to overstate what capital can actually earn | Anchored to a realistic redeployment rate |
| Market convention | The quoted standard in venture, private equity, and real estate | Less familiar; usually shown alongside IRR |
When IRR is the right tool
IRR remains the language of the market, and there is little avoiding it when term sheets, fund track records, and hurdle rates are all quoted that way. It is reasonably trustworthy for a conventional pattern, a single investment followed by inflows, when the computed rate lands near plausible reinvestment opportunities. For moderate returns over ordinary holding periods, the gap between IRR and MIRR is typically too small to change a decision.
When MIRR is the right tool
MIRR earns its place when a venture or project throws off substantial interim cash, or when the computed IRR sits well above what redeployed capital could plausibly earn. Compounding inflows forward at an explicit reinvestment rate and discounting outflows at a financing rate produces one unique answer even when repeated sign changes can leave the IRR equation with several candidate roots. Presenting a 30 percent IRR next to a MIRR built on a defensible reinvestment rate shows exactly how much of the headline depends on the reinvestment assumption.
The common mistake
The recurring mistake is treating a high IRR as the rate at which the investor's entire commitment compounds. A deal that returns capital in year two and reports a 40 percent IRR has implicitly assumed those early dollars keep earning 40 percent somewhere else, an opportunity that rarely exists. The inflated figure then anchors negotiations and cross-fund comparisons. Recomputing the return as a MIRR at a defensible reinvestment rate generally shrinks the number and reveals how much of the headline was assumption rather than cash.
Work the numbers yourself
Both concepts are taught in depth, with practice questions, in the free Entrepreneurial Finance course.