Nothing worse than going it alone with unstable cash flow to only see something as critical as health insurance costs double/triple/quadruple (pick your multiplier).

Better to have a month's vacancy than to suffer multiply months of no rent while having to deal with evictions.

I know when wholesaling a single family house, you make sure to deduct the 4% from the end buyers purchase price..Do I multiply 4% x 6 and deduct that from the purchase price ?

Deceive the seller and watch your problems multiply!

Multiply that by 20 and you will be in serious trouble.

I make sure the sq. feet is within 150 of each other, and I make sure the year built is close together.After that I calculate the average price per sq. ft. of the comps and multiply that by the sq. ft. of the property.  

I think the inherent flaw in your calculation is adding your "profit" after already multiplying by .70 Your profit is in already the 30% spread.

So if we have $75,240 in annual income, multiply that number by (1-0.45) 0.55 to get an estimated NOI of $41,382. 

(Actually, that'd be really cool if practical: some sort of multiplier to apply to his numbers for major metro areas.

Investing is about multiplying your money, right?