RSU Tax Calculator

Why RSU withholding comes up short

When RSUs vest, the share value is ordinary wage income, but payroll systems treat it as a supplemental wage and withhold federal tax at a flat 22%. Your salary has already filled the lower brackets, so the vest income sits on top and gets taxed at your highest rate, commonly 32% to 37% for people with meaningful equity. The 10 to 15 point difference on every vest quietly accumulates all year. Nobody sends a bill until you file, and by then the underpayment penalty may already apply, because the IRS expects its money during the year, not in April.

The cleanest protection is the safe harbor rule. Pay 110% of last year's total tax through withholding and estimated payments and no penalty can apply, no matter how large this year's vests are. The safe harbor calculator turns last year's return into that number in seconds.

From the gap to a real quarterly plan

This page prices the RSU layer by itself. Your real position also depends on capital gains from shares you sold, dividend and interest income, deductions, and what has already been withheld. The full calculator combines all of it, checks both IRS methods, and gives you the exact payment for each quarter, federal and state.