Discounting in financial mathematics is more complex than it seems. The Internal Rate of Return (IRR) is the discounting rate that makes the Net Present Value (NPV) zero. By using trial-and-error, we can find the IRR, which gives both negative and positive NPV rates. The Modified Internal Rate of Return (MIRR) compares the initial outlay with the project's net cash flows reinvested at the required rate of return to find the rate of return that yields an NPV of zero.