How do I calculate mortgage for BRRRR

[Chris Zolman]

I am very new to real estate. I haven't bought anything, I'm just working on my analyzing abilities. Here's my questions:

1. I've heard that a lot of mortgage calculators are not accurate. How do you analyze the initial deal if you don't know what the monthly payment will be for the mortgage?

2. when you go to refinance the deal, won't that make the mortgage payment higher than the original one? What happens if the rental income isn't enough to cover the mortgage?

is it possible to calculate the refinanced numbers before you even buy the property?