Mortgage Affordability Question

[Rachel Kim]

I am having difficulties understanding how investors can get more financing after the first or second property. I am not talking about coming up with the downpayment but rather regards to mortgage affordability.

A hypothetical situation when I enter in one of the banks' mortgage affordability calculator:

Annual Household Income: $100,000
Downpayment: $50,000

It says, mortgage amount approved with default insurance is $711,129 with a monthly mortgage of $3,380.

What I don't understand is that, if I wanted to buy a second property of $500,000 with the same household income, how would it work? It seems that a lot of investors are buying a lot of properties with refinancing, but I don't quite comprehend how they can just add more properties (given that they do have the downpayment) with a similar income.

Once I have $700,000 property (3 plex, one of the floors we live and 2 units rented out at $2000x2 = $4000, and the mortgage of $3380) with the same household income, how can one add more properties given that I have the downpayment for the next property (not waiting next 5 years to pay down the equity)?

If would be very appreciated if I can get some clear answers to this. Thank you and happy holidays!