The highest tax bracket for estates and trusts for the tax year is 37%, which applies to taxable income above $12,750 for single filers and $25,500 for married filing jointly. However, the net investment income tax of 3.8% applies to the net investment income of estates and trusts that exceeds the threshold amount of AGI. The threshold amount for estates and trusts is $25,400 for the tax year. The instructions for Form 8960 provide detailed information on how to calculate taxable income and the net investment income tax.