Because Georgia follows federal AGI, a traditional 401(k) lowers both taxes at once. Suppose the $70,000 worker defers 6% of pay, $4,200.00 a year. Georgia income tax falls from $2,744.50 to $2,534.92, and federal income tax from $6,570.00 to $5,716.00.
The upshot is that putting $4,200.00 into the plan reduces take-home pay by only $3,136.42; the rest is tax that would otherwise have gone to Washington and Atlanta. Social Security and Medicare are unchanged, since FICA applies to deferrals too. Enter a percentage under “Traditional 401(k)” above to try your own figure.