what is your formula to analyze a rental investment? 

@Michaelmy apologies some times it takes me a little bit to answereasiest way to explain formula for youArv is After Repair Value meaning after full renovation or repairs this is what the house will sell for 30-60 days max based on comparable sales (aka comps)I prefer lower 60% of the ARV, because I prefer to flip to a retailer, by wholesaling, and earning a small fee for finding the deal and securing the property via purchase agreement option or a few other various formsmost of my ppl buy at 65% or 70% so due to my preferred method of wholesaling, I must buy at prices below these "strike prices" or buy prices...just so you know I am a contractor, so my repair costs are known when I look at property.

If you're buying for cash flow I'm not sure what value ARV has in such formula.

Encinas  That's a quick helpful formula. 

I know you need a positive ROI...is there a formula somewhere I could start applying to some theoretical deals?

Paul, I'd advise looking for a realtor who owns properties already and understands the dynamics of the actual formulas on costs/expenses as you will need guidance on a lot of details. 

In CA, you won't be accorded that, we modify our formula here as MAO = ARV - 10% ARV(holding/selling costs) - Profit Goal - Purchase Price.

Their formula is to buy cheap homes in lower middle class areas, renovate, rent and resell to investors.  

I got and understand the formula.

I just use the tax assessors calculator and it explains all the formulas.