Mathematically, it doesn't matter if you have this done with one loan that you held for 365 straight days, or 2-3x on shorter-duration loans as you outlined above.To make that more intuitive, even if you reinvest 3x a year... each of those investment periods will only be for less than a full year, right?

Mathematically they could do 10+ projects but we settled on 8.

At that amount, even though it's the same risk equation mathematically, I would probably pass because of what other ways I could invest $250-500K vs a lesser amount like $3,000. 

Now I am no genious, but I am certainly proficient in mathematics and a 385k loan at 10% interest is $3208.33 of interst alone, let alone the principle!

I always despised those flippant little sections of finance texts that summarily discounted the value of IRR because it has more than one solution in some cases or isn't a perfectly elegant mathematical solution.

I even disagree with my friend @Ned Carey, which is the first time that happened...In mathematical terms, I would tell you to underwrite to IRR.

The difference between the average daily balance of the HELOC by depositing ALL your income into it - and using it as a checking account is what does the trick.The fundamental mathematical principle is not "paying extra on principal" it is REDUCING ACCRUED INTEREST - which results in more money going toward principal. 

Mathematically, not every house will be a winner.

Hi @Eric Li,Mentality: You and I are very much alike; you are very analytical, which is a gift, but it also can trick you into thinking you can outsmart the future and mathematically win at investing. 

For example, you might want to seriously consider doing some direct marketing to owners of small multi's in your city, especially those that look like they might be poorly managed, or have an absentee owner.It's going to be challenging getting ahead when paying 100x mthly rents for small multi's at this rent point, that's just a mathematical reality.