Real estate is impacted by macro factors but is ultimately hyper-local. 

there are a lot of new development coming up in the area.

Acting on that deal depends on a number of factors for me.  

Net $620 or $155 per door, meets Brandon's $100 minimum per door.However, based upon the post, I don't think all the expenses are factored in.Terry

You need to develop your own, because if you don't you will be less confident when you buy, if you buy at all.  

Two big expenses that really factor into decision making.

But how do I factor in the potential of adding units?

To me, that tells me it's a "guess" based on "fudge factors" which are based on "nothing" because of the lack of actual facts within the "fudge factors", and lack of any true analysis within the "rule".Third, if the rule has no real basis of facts, or analysis, and is not really a rule in the first place (or the 2nd place, in my order), then I'd say the 70% Rule is about 0% realistic...give or take 70%.

I am a web developer living in San Diego, California area and have a long time interest in real estate, but have not jumped in as of yet.

There's a different risk factor for those.Overall, I do feel like the highly experienced investors are underserved by lenders right now and that there isn't really a good product out there for them.