Illinois Supplemental Tax Regulations for Amazon RSUs
Illinois applies a flat 4.95% individual income tax rate with matching 4.95% supplemental withholding.
Illinois Safe Harbor & Underpayment Penalties
IL-1040-ES safe-harbor required if unpaid tax exceeds $1,000.
Employer Stock Plan Specifics: Morgan Stanley at Work (Shareworks) / Fidelity
Amazon equity packages are heavily backloaded into years 3 and 4 (40% each year). In year 3, your total W-2 income can leap into the 37% marginal bracket, while Morgan Stanley only withholds 22% federally. Without quarterly estimated payments or selling additional shares, Amazonians face a $15,000–$40,000 tax shock in April.
When vesting at Amazon, Morgan Stanley at Work (Shareworks) / Fidelity calculates automatic sell-to-cover withholding using Illinois's statutory supplemental rate of 4.95% combined with the federal supplemental rate (22% on up to $1M). Because top earners in Illinois reach marginal brackets exceeding these rates, you will face an incremental shortfall on April 15.
Localized CPA & Advisory Referral
Advisor Guidance: Work with a Chicago CPA to coordinate Illinois IL-1040-ES payments for large technology RSU vests.