When someone dies, their assets become property of their estate. Any income those assets generate is also part of the estate and may trigger the requirement to file an estate income tax return. Examples of assets that would generate income to the decedent’s estate include savings accounts, CDs, stocks, bonds, mutual funds and rental property. IRS Form 1041, U.S. Income Tax Return for Estates and Trusts, is required if the estate generates more than $600 in annual gross income.