Thank you DoninGA. I forgot the that tax tables goes by $50 increments rather than using the actual formula set forth in the Internal Revenue Code. The tax table is mandatory for income under $100,000. That is what caused the jump in my tax liability. I am being taxed as if I had an additional $50 of income, rather than the actual additional $13 of income.
IRC 3(a)(1) gives the IRS the right to prescribe tax tables but goes on the say: "In the table so prescribed, the amounts of the tax shall be computed on the basis of the rates prescribed by section 1." Since under the tables, $1 of additional income could result in $12 of additional tax, a marginal rate I don't find in the Code, hard to see how that is computed "on the basis of the rates prescribed by section 1."
I guess I could file in tax court for a $9 refund and see what happens. A fun way to spend my golden years as a retired tax lawyer.
