How is DTI calculated and when am I safe to buy another door?

[Page Weil]

How do underwriters calculate DTI when I have several leased rental properties? This may seem like an obvious question, but my last experience is that there is more to it than [rent payments] - [PITI] - [1% repairs]

I have access to a lot of credit I can use for outright purchases of rentals but I only want to buy properties if I can refinance them immediately. I don't want to buy a property with a handshake agreement that a bank will give me a loan, I want to be able to calculate the DTI the bank cares about and see when I am near that target.

Income:

[Day Job]

[Schedule C side business]

[Rental Income 1]

[Rental Income 2]

[Rental Income 3]

Debts

[Primary Mortgage]

[Rental Mortgage 1]

[Rental Mortgage 2]

[Commercial Loan for Mort 3]

[Minimum HELOC payment]

How would an underwriter actually use these pieces to come up with a decision on whether they would loan to me?