@Ken Primrose the quickest, back of the napkin way of analyzing a deal is by using the 50% rule. The 50% rule assumes that there expenses will be ~ 50% of a properties NOI (Net Operating Income).
So let's say the average rent of a 100 unit apartment is $1,000/m.
100 X $1,000 = $100,000 X 12 (months) = $1,200,000 of GPR (gross potential income). Not accounting for vacancy OR other income.
$1,200,000 X .5 = $600,000 of NOI
Now let's say the purchase price is $12,000,000 (NOI at a 5% cap rate) and you will get a 75% LTV loan with a 3% interest rate with at least one year of interest only.
$12,000,000 * .75 = $9,000,000 in loan proceeds X .03 = $270,000 of an interest only payment (NON AMORATIZING)
That will leave net cash flow NOT including capex, RR deposits, AM fees, etc of $330,000.
Let's also assume your required equity = 30% of the purchase price with down-payment, third party reports, lender fees, closing costs, etc. So let's assume 30% of purchase price for equity = $3,600,000
For cash on cash assuming no changes to operations $330,000/$3,600,000 = 9.1% cash on cash
9% is a pretty good cash on cash. Now I would do a more in depth analysis that takes into account actual financials, incorporating your business model, including all line items, etc.
There are many flaws in this method, but it can be better than nothing.