Deductions & credits

My wife's TT determined max contribution amount is understandable.  But mine isn't because I am disabled and my only sources of income is from SSA disability payments, my Gov't retirement pension, and no taxable interest, dividends, or capital gains.  So I would think my max contribution determination would be 0.  But TT comes up with $1,492 for me.  I would like to see how this number is generated.