Where it really adds up (multiplies) is with appreciation, depreciation, and mortgage pay down.

@Bryson Gilbert take the total sqft and multiply it by $35/ $40 ( this is how we do it in Texas).

@Jeegar Patel it's not exact, of course, but I usually just take the primary residence taxes and multiply them by 3.5 in Richland County where I buy my properties.

But be carefull, loans tend to multiply when you do not control your financial sutiation and you will have to take more and more to close previous ones and you will end with almost nothing but only debts.

Leverage just multiplies gains or losses.So, I'd say, if they're good properties and you anticipate gains then consider it regardless of age.

It’s a percent calculation of assessed land and property value multiplied by the purchase price.

Original cost (maybe per the appliance company previously mentioned)Multiplied by (11/estimated useful life).You absorb the rest.

I’ve come across he formula for dealing with Gross Rent Multiplier, which is the selling price of the property/gross rent per year. 

I don't currently have the capital so I'm spending my time educating myself and saving every dime and investing what I save to multiply it.

If there aren't comps there I personally would value the property relative to its potential rental income using either the gross rent multiplier or cap rate method.