I'm trying to calculate and solve my historical and future projected monthly yield factoring in time for my litigation funding company. I began this project thinking that Internal Rate of Return (IRR) would be the correct formula to use. I can't use the normal IRR function in Excel since it can only handle one negative number in a fixed stream of cash flows. Excels Modified Internal Rate of Return (MIRR) formula allows for multiple negative cash flows, but I'm not clear if this is the correct formula to use for my purposes. I'm told that when using MIRR, for every negative sign change beyond one, that there are additional correct answers (ex: if they're four sign changes there would be four mathematically correct answers for the IRR).
I need you to help me determine the following once I bring you up to date:
Is MIRR adequate for my needs? How should investor capital infusions into my company be accounted for? Do I need to create a special formula for my unique needs? If so, you would need to have the mathematical capacity to create this formula.