"Lowering the bracket" isn't really the goal. Rather, contributing enough money into a deductible IRA that SAVES the most income tax before contributing MORE saves LESS.

How about this: the taxable income is $8,250 over the bottom rung of the 24% bracket(Single, $100,526); therefore, putting $7,000 into the IRA saves 24% of the $7,000, but it does not "lower the bracket." Any other income will be taxed at 24%.

Better example: the taxable income is $4,250 over the bottom rung of the 24% bracket; therefore, putting $4,250 into the IRA saves 24% of the $4,250, but adding $2,750 more to the IRA saves only 22% of the extra $2,750.

{Not counting any changes due to the lowering of AGI with the IRA.}