Internal Rate of Return (IRR) Calculator

About the Internal Rate of Return (IRR) Calculator

The Internal Rate of Return (IRR) is the discount rate that makes the Net Present Value (NPV) of a cash flow series equal to zero. In simpler terms, IRR is the annual return an investment generates over its life, accounting for the time value of money.

If a project's IRR exceeds the company's cost of capital (WACC), the project creates value and should be accepted. If IRR < WACC, the project destroys value. For example, a project with 15% IRR and 10% WACC earns 5% above the minimum required return.

This calculator uses iterative bisection to solve for IRR, validates the result with NPV verification, and includes MIRR (Modified IRR) for projects with non-conventional cash flows. While IRR has some limitations and can give misleading results for projects with unconventional cash flow patterns, the Modified IRR corrects these by assuming reinvestment at a more realistic rate. Together, IRR and MIRR give you a clear, percentage-based measure of investment attractiveness that complements NPV analysis.

When This Page Helps

IRR is the most widely used metric for judging project and investment attractiveness. It expresses return as a single percentage, making it easy to compare across different investments. Combined with NPV analysis, IRR provides a complete picture of whether to accept or reject a capital allocation decision. Together, they give you the most reliable framework for evaluating any investment opportunity.

How to Use the Inputs

1. Enter the initial investment as a negative cash flow in Year 0.
2. Enter expected cash flows for each subsequent year.
3. Enter your WACC or required rate of return for comparison.
4. View IRR, NPV at WACC, and accept/reject recommendation.
5. Check MIRR for a more conservative return estimate.
6. Add or remove years to match your project horizon.

Example Calculation

Tips & Best Practices

• Always check NPV alongside IRR. IRR can give misleading rankings for mutually exclusive projects of different sizes.
• IRR assumes reinvestment of interim cash flows at the IRR rate — this is often unrealistic. MIRR uses a more realistic reinvestment rate.
• Non-conventional cash flows (sign changes beyond the initial) can produce multiple IRRs. Use MIRR in those cases.
• IRR doesn't account for project size. A $100K project with 50% IRR adds less value than a $10M project with 20% IRR.
• For comparing projects of different durations, use Equivalent Annual Annuity (EAA) or chain the shorter project.
• An IRR of exactly 0% means the project returns exactly its invested capital with no gain or loss.

The IRR Calculation Process

IRR cannot be solved algebraically for more than two periods. Instead, iterative methods (bisection, Newton-Raphson) try different discount rates until NPV equals approximately zero. This calculator uses bisection: it narrows the IRR range by testing the midpoint and selecting the half where the sign changes.

NPV Profile

Plotting NPV against various discount rates creates the NPV profile. Where the curve crosses zero is the IRR. For conventional cash flows (negative initial, then positive), the curve slopes downward from upper-left to lower-right. Multiple zero-crossings indicate multiple IRRs.

Practical Decision Rules

For independent projects: accept if IRR > WACC. For mutually exclusive projects: pick the one with higher NPV (not necessarily higher IRR). For capital rationing: rank by Profitability Index. Always run both IRR and NPV before making capital allocation decisions.

Frequently Asked Questions

• IRR vs NPV: which is better?

  Both are valuable. NPV shows absolute value creation in dollars. IRR shows the return rate. For accept/reject decisions on independent projects, they always agree. For ranking mutually exclusive projects, NPV is more reliable because IRR can favor smaller projects with higher percentage returns.

• What is MIRR and when should I use it?

  Modified IRR (MIRR) addresses IRR's two flaws: (1) the unrealistic reinvestment assumption and (2) multiple IRR solutions. MIRR uses a realistic reinvestment rate for positive cash flows and a finance rate for negative flows. It always gives a single solution. Use MIRR when cash flows change sign multiple times.

• Can IRR be negative?

  Yes. A negative IRR means the project loses money. An IRR of −10% means the project destroys 10% of the initial investment annually. This happens when total cash inflows are less than the initial investment, even ignoring time value.

• What's a good IRR?

  It depends on the risk and opportunity cost. The minimum acceptable IRR is the WACC (typically 8-12% for most companies). Venture capital targets 25-35%+ IRR. Real estate targets 12-20%. A good IRR exceeds your hurdle rate by a comfortable margin to account for estimation error.

• Why might a project have multiple IRRs?

  Multiple IRRs occur when cash flows switch signs more than once (e.g., invest, earn, invest again). Descartes' rule of signs: the number of positive real IRRs cannot exceed the number of sign changes. In these cases, use MIRR or NPV profile analysis for the decision.

• How does IRR handle different project lengths?

  IRR doesn't directly adjust for different time horizons. A 3-year project with 20% IRR may or may not be better than a 10-year project with 15% IRR — it depends on what you can earn after the 3-year project ends. Use NPV with a common time horizon for comparison.