Why do you have to pay Federal Income Tax on an annuity you received after your father's death?
The money you receive from the annuity is income. All income is supposed to be reported and taxes paid on it.
It depends upon where that money came from in your fathers estate. If this annuity came from your fathers annuity which was established from IRA or a 401K which had never paid taxes on -then the annuity now needs to pay the taxes.
If the annuity came from life insurance then their is no taxes to pay. If the annuity came from prepaid tax money there would be no taxes to pay. etc.