I have been unable to work for well over the past year due to physical and mental conditions. So I think I (as the spouse) hit the 2 points about being unable to engage in substantial gainful activity for a condition that has lasted for at least a year.
My questions are:
1) What benefit does this give, if any? Is there a credit or deduction that would apply? Or is this just asked due to potential for having social security income that needs to be listed (which I don't receive)?
2) Do I need to get an actual doctor letter for this?
The only benefit is if you paid for someone to care for her to enable you to work.
there may also be credit for being disabled - Schedule R if all the criteria are met.
For disabled adults:
There is an extra amount added to your standard deduction if you are legally blind. Your federal return does not provide any other credits or deductions for saying you are disabled, with one possible exception.
There is a credit for the Elderly and Disabled which is so small that very few people benefit from it—-it has not been updated/increased by Congress for decades.
ELDERLY OR DISABLED CREDIT https://www.irs.gov/help/ita/do-i-qualify-for-the-credit-for-the-elderly-or-disabled
There are some states that provide various credits to elderly/disabled folks, so watch for that when you prepare your state return. The states that I know of that have anything for elderly/disabled are AZ, CT, DE, IA, MO, ND, NJ, NY, VE. There may be others.
1. Benefit- increased deduction. Possibly credit for the disabled and/or child care credit. Child care credit would not be allowed unless you marked disabled without employment income. See About Form 2441, Child and Dependent Care Expenses and About Schedule R (Form 1040), Credit for the Elderly or the Disabled
2. You don't need a doctor's letter to file your return. If the IRS asks for substantiation, then you would need to provide proof.