Yet another 1099-R question

[thompson-melissa]

Ok- so MIL passed 3/29/20. Apparently she left money to both husband and my SIL. We received a 1099-R form in 2020 which I added to my taxes. Box 7 was marked 4 for death. Box 2b was marked taxable amt not determined and total distribution. And the IRA/SEP/SIMPLE box is checked. Now I paid an extraordinary amount of taxes on this. But recently was told that I may have filed something incorrectly as I may not have had to file taxes. Can someone help explain this? 

Additional info not sure if important MIL was 72 1/2 when she passed. 

[Mike9241]

sorry for your loss. you would need your MIL tax return for the year prior to death and year of death if she took an IRA distribution before she died and had tax basis in her IRAs that amount would show up on line 14 of form 8606.

also if the amount was from ROTH IRAs the amount received would not be taxable

otherwise for non-ROTH IRAs

• At death, IRAs do not get a step-up in basis. The owner’s basis is passed down to the IRA beneficiary without any basis adjustments.

[thompson-melissa]

@Mike9241  Thank you. 
She did not take out any distributions.