Massachusetts Supplemental Tax Regulations for Microsoft RSUs
Massachusetts withholds at the standard 5.0% flat income tax rate. However, under the Massachusetts Fair Share Amendment, taxable income above $1,000,000 is subject to an additional 4% surtax (total 9.0%), creating a 4% withholding shortfall on multi-million dollar vests.
Massachusetts Safe Harbor & Underpayment Penalties
Submit Form 8488 or quarterly Massachusetts estimated tax payments.
Employer Stock Plan Specifics: Fidelity Investments
Microsoft employees in Redmond, WA enjoy 0% state income tax on vesting wages, but face the full federal marginal spread. For senior SDEs and Partners whose base exceeds the $184,500 Social Security cap, every incremental vest dollar is taxed at 35% or 37% plus 2.35% Medicare.
When vesting at Microsoft, Fidelity Investments calculates automatic sell-to-cover withholding using Massachusetts's statutory supplemental rate of 5.00% combined with the federal supplemental rate (22% on up to $1M). Because top earners in Massachusetts reach marginal brackets exceeding these rates, you will face an incremental shortfall on April 15.
Localized CPA & Advisory Referral
Advisor Guidance: Find a Boston tech CPA experienced with the Massachusetts 4% Fair Share Amendment ("Millionaire's Tax") on high equity vests.