Claiming Income from Secondary Home STR on Future Mortgages?

[Jason L.]

I'm looking at buying my first STR in the near future using a secondary mortgage. My goal is to then hopefully buy a new primary at some point afterwards in 2022. My lender is unsure if income from a secondary home would be permissible to be written off against the mortgage when I went to try to apply for the new primary. To be clear, I know that future income can't be used when buying the secondary home itself, but I'm talking about using the receipts after buying the secondary to show additional income when I went to buy the primary later on. Can anybody help us out here?

Furthermore, if it is allowed to be written off, how long do I need to be able to show AirBnB receipts for before a lender would accept it as income? Would I have to wait for the following year's tax return or can it be done sooner?