Here is what I found, seems to be reasonable based on past experience with this type of calculations.
Definitions
Monthly income: Total monthly income from all sources. All income should be entered before taxes.
Monthly housing expenses: Your monthly housing expenses from the housing expenses worksheet. The items entered as housing expenses make up the taxes and insurance portion of your monthly housing payment.
Monthly liabilities: Your monthly liabilities from the liabilities work sheet. Your monthly liabilities are used to calculate your maximum monthly house payment.
Monthly housing payment (PITI): This is your total principal, interest, tax and insurance, or PITI, payment per month. This includes your principal, interest, real estate taxes, hazard insurance, association dues or fees and principal mortgage insurance, or PMI. Maximum monthly payment (PITI) is calculated by taking the
lower of these two calculations:
- Monthly Income X 28% = monthly PITI
- Monthly Income X 36% - other loan payments = monthly PITI