In an ad valorem system the rate floats so that enough revenue is generated from the ratables to satisfy the municipality's budget.The assessment may/will change if the Assessor decides to modify the municipaliy's assessment by either adjusting everbody a percentage by the property value appreciation across the area. 

It would be a useful tool for members and it would generate revenue for BP, allowing you to continue producing awesome content.

Almost no setup costs and guaranteed increase in revenue. 

Anyway, plug in the revenue and expesnses for both models. 

I use a free online software program (wave) which connects to my bank accounts and allows me to categorize all revenue and expenses.

@Axel MeierhoeferIf you buy a property, and your chief source of revenue through the property is the rent your tenants pay, and the only way you can significantly increase your revenue is by significantly increasing the amount you make them pay, then your chief business strategy and goal is, simply, TO SUCK AS MUCH MONEY AS YOU CAN FROM YOUR TENANTS.

In many situations, the revenue earned from the other rooms or units will NOT completely cover your mortgage payment and expenses, and that's ok.

It seems there are a number of sources to estimate revenue.

Joe V is still correct, as others as well, that these numbers added to your mortgage expenses and property management fees (typically 8-10%) only help you as an initial starting point and remove a lot of revenue/gross income from the property equation.

it's not just the rental itself you're buying, it's also the space and knowing what you can add to amplify the revenue. it can make a marginal deal look solid if you know what to do with it.