How 401(k) Contributions Work in Illinois
A pre-tax 401(k) contribution reduces your adjusted gross income dollar-for-dollar at the federal level. In Illinois, contributions also reduce your Illinois state taxable income at the 4.95% rate. On the state's median household income of $83,211, contributing 6% ( $4,993/year) saves $1,098 in federal tax (22% bracket) plus $247 in state tax — a combined $1,345/year reduction in your tax bill.
The formula for your projected 401(k) balance uses month-by-month compounding:
Monthly interest = Balance × (Annual Return ÷ 12)
New Balance = Balance + Monthly Interest + (Employee + Employer Contribution) ÷ 12
Example for Illinois: Contributing 6% of the $83,211 median income ( $4,993/year) with a typical 100%-match-up-to-3% employer match ($2,496/year) = $7,489/year combined. At a 7% annual return over 30 years, that grows to approximately $761,364 — generating roughly $30,455/year in retirement income under the 4% rule. The employer match alone ($2,496/year at 7% for 30 years) accounts for approximately $3,045,048 of that total.
Illinois Retirement Tax Status: Retirement income exempt
The tax treatment of 401(k) withdrawals at the state level directly affects whether a Traditional or Roth 401(k) is more advantageous for Illinois residents. Illinois exempts retirement income from state tax, meaning Traditional 401(k) withdrawals avoid the 4.95% state income tax entirely. This creates an asymmetric advantage for Traditional contributions: you get the full 4.95% state deduction today but pay zero state tax on withdrawals later.
2026 IRS 401(k) Contribution Limits
The IRS sets contribution limits uniformly — they are the same in Illinois as in every other state:
- Under age 50: $23,500/year employee elective deferral
- Age 50–59 and 64+: $31,000/year (includes $7,500 catch-up)
- Age 60–63: $34,750/year (SECURE 2.0 higher catch-up of $11,250)
- Total plan limit (employee + employer): $70,000/year