as a value RE investor, I think positive cash flow is the most important key.
there really isn't a good or bad time to buy real estate, the only thing it matter is, what is your entry point and what is your exit strategy.
in an up trend market, I only make a move when there is a 30-40% spread, in a down trend market, I need to see at least 50+% discount.
the 3 most frequently used ratio are, debt coverage, CAP rate, and cash on cash.
1. when I look at a property, I always use zero down, NOI/(interest to bank + interest to me)>=1.1
2. CAP, of course, I need to see 10% CAP.
3. CASH on CASH, 15% or more.
NPV, IRR, easy to do on paper, but in reality, hardly can be followed. RE as a small business, has too many unforeseen variables, any unexpected repair can wipe out the whole cash reserve.
