I would run comps on zillow, check out BP calculator to run numbers and Rent-O-meter to check average rent. 

More on how that is calculated below.

We chose HELOC instead of refi because we didn't want the rates to change (we got the first property during those golden days of 3% interest).I just recommend making sure the HELOC payment makes sense from a numbers perspective—consider the interest as another "expense" when you're calculating cash flow.

So, when doing my calculations in the AirDNA calculator I should leave this expense off even though it has a place for this. 

And don't forget to think about property management, whether you plan to handle it yourself or hire a professional company.Before purchasing your first rental property, it is important to conduct a detailed financial analysis using tools like real estate investment calculators or spreadsheets.

If you have any questions on the calculations or a strategy, please ask me.

Best regards,CharleyTom Henderson has the note calculator course and Bill Mencarow, from PaperSource, has some courses   Those are good programs to begin with   

You can calculate this very easily. 

I was trying to create a BP calculator for a client but it will not let me upload a pic of the property. 

Vacancy should be calculated into your underwriting.