Mother in law passed in 12/2018, she received interest income from the sale of bonds from the treasury but not until 1/2019. Need to file for the interest income.

Note: If the estate yearly  income is less than $600, no estate tax return is needed.

IRS Pub 559 --

"If the decedent accounted for income under the cash method, only those items actually or constructively received before death are included on the final return.

Income in Respect of a Decedent

All income the decedent would have received had death not occurred that was not properly includible on the final return, discussed earlier, is income in respect of a decedent.

How To Report

Income in respect of a decedent must be included in the income of one of the following.

• The decedent's estate, if the estate receives it.
• The beneficiary, if the right to income is passed directly to the beneficiary and the beneficiary receives it.
• Any person to whom the estate properly distributes the right to receive it."