RSU tax in Massachusetts

A $60,000 vest costs $3,000 in Massachusetts tax on top of the federal bill. And the federal share withheld is $2,970 short.

What a $60,000 vest actually costs in Massachusetts

A single filer already earning $180,000 in salary. The vest stacks on top of that, so it fills the highest brackets rather than starting at the bottom:

Withheld by your employer at 22.0%	$13,200
Federal tax the vest actually costs	$16,170
Federal shortfall, owed in April	$2,970
Massachusetts income tax on the vest	$3,000
Total still to find	$5,970

The withholding rate is flat, 22.0% below $1 million of supplemental pay. And takes no account of your salary. That is why the gap grows the more you earn.

The gap widens with salary

Salary	Withheld	Actually owed	Shortfall	Massachusetts tax
$90,000	$13,200	$13,764	$564	$3,000
$160,000	$13,200	$14,570	$1,370	$3,000
$260,000	$13,200	$20,630	$7,430	$3,000

How Massachusetts treats a vest

Massachusetts taxes a vest as ordinary income like any other wages, adding $3,000 on top of the federal bill for $60,000 of vesting stock.

Massachusetts is one of the states that sources equity income aggressively. If any part of the vesting period was worked here, Massachusetts will claim its share of the vest even if you had moved away by the time the shares actually landed. Days worked in each state / total days in vesting period x RSU income = each state's allocation

What the same vest costs around Massachusetts

Total income of $240,000 in the states Massachusetts borders:

State	Its tax	vs Massachusetts
New Hampshire	No income tax	−$12,000
Rhode Island	$11,571	−$429
Connecticut	$13,350	+$1,350
New York	$13,924	+$1,924
Vermont	$15,784	+$3,784

New Hampshire has no income tax at all, so the same work done there costs $12,000 less in state tax than it does in Massachusetts.
Rhode Island would take $429 less, $11,571 against Massachusetts's $12,000.
Connecticut would take $1,350 more, $13,350 against Massachusetts's $12,000.
New York would take $1,924 more, $13,924 against Massachusetts's $12,000.
Vermont would take $3,784 more, $15,784 against Massachusetts's $12,000.

RSU questions in Massachusetts

Should I sell at vest?

Selling immediately raises the cash for the $5,970 you still owe and leaves no capital gain, because the sale price equals the price you were already taxed on. Holding turns it into an investment decision, any further gain is a capital gain, and any fall is a loss you take on shares you were already taxed on at the higher value.

I moved to Massachusetts mid-vest, who taxes it?

Both states, split by workdays. The income is allocated across the vesting period, not assigned to wherever you happened to live on the vesting date. The state you left can still claim its share, and California, New York and Massachusetts pursue it hardest.