If one spouse uses “married filing separately” as the filing status, the other spouse must also use this filing status. The other spouse must file if his/her gross income is more than a set amount. For 2017 returns, this amount is $4,050.
Debt secured by a principal residence or second home to the extent of the excess of fair market value over acquisition debt. An interest deduction is generally allowed for home equity debt up to $100,000 ($50,000 if married filing separately).