Net rental income is considered qualifying income when applying for a mortgage, as it represents income generated from rental properties. Lenders typically calculate net rental income by subtracting property expenses from the total rental income, and they require documentation such as tax returns or lease agreements to verify this income.

Reimbursed expenses (A), family gifts (C), and federal tax refunds (D) are generally not considered qualifying income, as they are one-time or non-recurring sources of funds.