@Voncella McIntosh I will try to explain the calculation as best i know it. Your approved monthly payment amount is approximately 30% of your combined income (your income and 75% of your estimated rental income). So if you make $5000 a month from your job and your total rental income on the 3 other units is $3000, your combined income would be $5000 + $2250 ($3k x 0.75) = $7250 so your approved payment would be $2175. But how do you know what the potential rent will be? You can either use the current rents (which the bank will do) or you can look at rental comps for that area. When you have the appraisal done, they will estimate the rental income value and you can fight it with comps if you feel it’s too low.
So now your monthly payment budget is $2175. This means your mortgage payment, interest, insurance, and taxes have to be $2175 or less to be approved. My spreadsheet does the calculation so you can easily see what the numbers are on specific properties and if the total fits the budget.
Let me know if you have any further questions.