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.
The tax on the investment income in excess of $1,700 (may change after 2007) of a child under age 18, based on the parents’ marginal tax rate and computed on Form 8615.