Here is copy paste from 1.163-8T
(d) Debt repayments—(1) General ordering rule. If, at the time any portion of a debt is repaid, such debt is allocated to more than one expenditure, the debt is treated for purposes of this section as repaid in the following order: (i) Amounts allocated to personal expenditures; (ii) Amounts allocated to investment expenditures and passive activity expenditures (other than passive activity expenditures described in paragraph (d)(1)(iii) of this section); (iii) Amounts allocated to passive activity expenditures in connection with a rental real estate activity with respect to which the taxpayer actively participates (within the meaning of section 469(i)); (iv) Amounts allocated to former passive activity expenditures; and
