Final answer:
Joan may not need to file a federal income tax return if her income of $20,500 falls below the filing threshold for her age and filing status. Other factors such as dependency status and other income sources also influence the necessity to file a return.
Step-by-step explanation:
When determining whether Joan, a 66-year-old widow, needs to file a federal income tax return, several factors must be considered. Her gross income is $20,500 for the year, but we must look at the standard deduction and filing threshold for someone of her age and filing status to determine if she is required to file. While exact numbers can vary year to year, generally, single taxpayers who are 65 or older have a higher standard deduction. If her filing status is 'qualifying widow(er)', she may have a higher filing threshold, making it possible that she may not need to file if her income does not exceed this threshold.
However, in other circumstances, such as the estate tax exemption for surviving spouses, it's important to note legal changes, such as the Supreme Court ruling in United States v. Windsor, which deemed DOMA unconstitutional. This granted same-sex married couples the same federal rights as opposite-sex couples, affecting federal benefits and taxes. The tax liability also depends on other factors, including whether someone else can claim Joan as a dependent, her exact age at the end of the year, and other potential income sources or credits. Without the full context of her financial situation, a concrete answer cannot be given, but Joan may fall below the threshold requiring her to file a federal return, assuming she has no other complicating financial factors.