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·Economy·14 min read·Wondy

Old 401(k) After Leaving a Job: Leave It or Roll It Over? The Math on All Four

Four options for a 401(k) from a job you left, the 20% withholding that turns a $50,000 check into $40,000, and three cases where an IRA costs you.

A check on a $50,000 401(k) arrives as $40,000. The missing $10,000 was withheld, and you have 60 days to replace it out of your own pocket.

You have four options with a 401(k) from a job you left: leave it where it is, move it into your new employer's plan, roll it into an IRA, or cash it out. Every rule below is federal and current for 2026, read from IRS pages on August 21, 2026.

State income tax is not modeled anywhere here, and states treat retirement distributions differently enough that the state column has to be yours. Every worked example runs on the same constructed $50,000 account unless the paragraph says otherwise, and none of this is tax advice.

Four options, and the one reason each wins or loses

Most of the money lost here goes to execution rather than to the choice itself. Leaving it, rolling it to the new plan, and rolling it to an IRA all keep the balance invested and untaxed. The expensive mistakes, mishandling the transfer or rolling away an exception you needed, can happen on any of those three paths. Cashing out is the only pick that costs money on its own. The four still have different edges.

Leave it where it is. The case for standing still is usually price. Institutional share classes and stable value funds exist inside plans and not in retail IRAs, and the Investment Company Institute puts the average expense ratio paid by 401(k) participants in equity mutual funds at 0.26% for 2024 against 0.40% industrywide. The case against is that nobody will remind you the account exists, and some plans pay former employees in a lump sum only.

Move it into your new employer's plan. The underrated one. A plan balance stays invisible to the backdoor Roth calculation (covered in the IRA section below), and it keeps the option of a 401(k) loan, which no IRA offers. The catch is that the receiving plan can refuse. The IRS says so: "Your retirement plan is not required to accept rollover contributions. Check with your new plan administrator to find out if they are allowed."

Roll it into an IRA. The default answer, and often the right one: a poor plan menu, a Roth conversion runway, or the plain fact that you will not keep track of a fifth account. It also throws away two things you cannot get back, both further down. Before assuming the IRA is cheaper, the mid-year checkup post shows where the expense ratio hides in a plan statement.

Cash it out. On our $50,000 example account, $16,404 of federal tax and penalty. Worth it only against something worse than that.

Settle one thing before anyone starts paperwork. If the account holds employer stock, get the cost basis first, because leaving that stock in the plan can qualify its growth for capital-gains rates instead of ordinary income. Rolling it into an IRA cancels that treatment permanently.

Why a $50,000 check arrives as $40,000

A distribution paid to you gets 20% withheld by law, and a direct rollover paid to the receiving account gets nothing withheld. IRS Topic 413 puts it this way: "Any taxable eligible rollover distribution paid to you from an employer-sponsored retirement plan is subject to mandatory income tax withholding (generally at a rate of 20%)." The 60-day clock starts the day you receive it. So the indirect route asks you to deposit money the plan is still holding.

Balance in the old plan                        $50,000
Mandatory federal withholding, 20%            -$10,000
Check that actually arrives                    $40,000

To defer tax on the whole balance you must
deposit into the receiving account in 60 days  $50,000
Cash you have to find somewhere else           $10,000

The IRS compresses it to one sentence: "If you do roll it over and want to defer tax on the entire taxable portion, you'll have to add funds from other sources equal to the amount withheld." That $10,000 is not gone. It is federal income tax already paid, credited on that year's Form 1040. But a distribution taken in March 2026 comes back as a refund around spring 2027, so you lend the government $10,000 for roughly a year, starting the week your paycheck stopped.

Deposit only the $40,000 and the shortfall becomes a distribution. For a single filer at a 22% marginal rate and under 59½, the $10,000 costs $2,200 in income tax plus $1,000 in additional tax, so $3,200 total, and $6,800 of the withholding comes back at filing. And the tax bill is the smaller half of it: $10,000 left invested at 6% for 25 years would have been $42,919.

The direct rollover version of all of that is one line. Nothing is withheld, the full $50,000 lands in the receiving account, and no clock starts. One rule that panics people does not apply here either: the limit of one rollover per year covers IRA-to-IRA moves only, not plan-to-IRA, IRA-to-plan or plan-to-plan.

An outstanding 401(k) loan is the exception with a longer fuse. Leave a job owing money to your own plan and the unpaid balance is offset and treated as a distribution, but a qualified plan loan offset can be rolled over until the due date of that year's tax return including extensions. An offset in 2026 stays rollable until April 15, 2027, or October 15 with an extension.

What cashing out $50,000 actually leaves you

Cashing out costs more than the 20% that was withheld, because the distribution stacks on top of your salary and pushes part of itself into the next bracket. Take a single filer, age 40, $92,000 salary, no exception to the early distribution rules. Using the 2026 brackets and the $16,100 standard deduction from Rev. Proc. 2025-32, the same figures behind the Roth versus traditional 401(k) breakdown, the arithmetic runs like this.

StepAmount
Taxable income before the cash-out, $92,000 salary less the $16,100 standard deduction$75,900
Room left in the 22% bracket, which tops out at $105,700$29,800
First $29,800 of the distribution at 22%$6,556
Remaining $20,200 at 24%$4,848
10% additional tax on the full $50,000$5,000
Total federal cost$16,404
Already withheld at source$10,000
Still owed at filing$6,404

You keep $33,596 of $50,000 before any state tax, and the $6,404 arrives in April, by which point the money is usually spent. That gap between withholding and the real bill is the same failure behind a surprise April balance, and the W-4 audit post is the version for people with only a paycheck. If the reason for cashing out is that you are genuinely out of money, price the alternatives first, because several of the emergency borrowing options cost less than a 32.8% haircut plus the forgone compounding. That $50,000 at 6% for 25 years would have been $214,593.

Dollars still inside a retirement account after moving the same $50,000 four different ways. The cash-out row hands you $33,596 of spendable money instead. Federal only, single filer, $92,000 salary, age 40, 2026 brackets.Direct rollover 50,000, Indirect done right 50,000, Indirect, 60 days missed 40,000, Cash out 0Direct rollover50,000Indirect done right50,000Indirect, 60 days missed40,000Cash out0
Dollars still inside a retirement account after moving the same $50,000 four different ways. The cash-out row hands you $33,596 of spendable money instead. Federal only, single filer, $92,000 salary, age 40, 2026 brackets.

When rolling to an IRA is the wrong move

Three situations flip the default advice, and two of them are irreversible once the transfer settles. The first is the age-55 separation exception, which lets you take money out of a plan before 59½ with no 10% additional tax. The IRS condition is that "the employee separates from service during or after the year the employee reaches age 55," and IRC section 72(t) attaches the exception to workplace plans rather than to IRAs. Picture the case that makes it real: you are laid off in March at 54 and turn 55 that November. You separated during the year you reach 55, so distributions from that employer's plan skip the penalty. From the layoff to 59½ is a little over five years; draw $40,000 in each of those five years and $200,000 leaves the account penalty free. Roll that same balance to an IRA first and the exception does not travel with it, so the identical $200,000 costs $20,000.

The second is the pro-rata rule, which reaches anyone running a backdoor Roth. That is the workaround for people who earn too much to put money in a Roth IRA directly: you contribute to a traditional IRA without taking the deduction, then convert it to a Roth, and because the money was already taxed the conversion should cost almost nothing. It stops working the moment you have pre-tax money in an IRA, because the IRS makes you convert a blend of pre-tax and after-tax dollars rather than the fresh contribution. Take a bigger account than our example: $200,000 of pre-tax 401(k), rolled into a traditional IRA in January, then a $7,500 nondeductible contribution converted the same week. Only 3.61% of the conversion is treated as the after-tax money, which is $271. The other $7,229 is taxable, and at 24% that is $1,735 of tax on dollars you had already paid tax on once. Employer plan balances never enter the calculation, so leaving the money in a 401(k) sidesteps it entirely.

Creditor protection also comes up, and it is the most oversold of the three. You will often read that money loses its shield the moment it lands in an IRA. In bankruptcy that warning is simply wrong: federal law exempts rollover dollars from the IRA cap entirely, so rolled money keeps unlimited protection. Outside bankruptcy it flips. A judgment or a lawsuit runs into the federal anti-alienation shield that covers workplace plans in every state, while an IRA relies on state law that varies. If your work carries real lawsuit exposure, that argues for keeping it in the plan. Claiming Social Security at 62 versus 67 is the other retirement decision with this same one-way character.

Plenty of accounts still belong in an IRA. Usually one condition on one side of this list settles which.

Destination
Reasons to keep it in a plan
  • You left that employer in or after the year you turned 55
  • You contribute to a backdoor Roth every year
  • Employer stock sitting on a low cost basis
  • A job with real lawsuit exposure
  • Institutional share classes or a stable value fund
Reasons the IRA is the better home
  • No low-cost index option anywhere in the menu
  • The plan pays former employees lump sum only
  • You want a Roth conversion runway
  • You want to set beneficiary terms yourself
  • A fifth account you will never look at again
One line applying to you decides more than any general ranking of the four options.

Under $7,000 the plan can move your money without you

Small balances do not wait for you to decide. SECURE 2.0 Act section 304 raised the involuntary cash-out ceiling from $5,000 to $7,000 for force-out distributions made after December 31, 2023, and the three bands behave differently. Above $7,000 the plan cannot push you out, so our $50,000 example account stays put. Between $1,000 and $7,000 the plan may move the balance into a safe harbor IRA opened in your name. Under $1,000 it may mail you a check, which arrives net of 20% withholding and turns into taxable income plus the 10% additional tax if you do not deposit it somewhere within 60 days. A different account entirely, a $900 leftover from a summer job, becomes a $720 check and a 1099-R you forgot was coming.

The middle band is worse than the bands make it sound. GAO-15-73, the Government Accountability Office's study of forced transfers and inactive accounts, found that fees outpaced returns in most of the safe harbor IRAs it analyzed, so balances shrank over time, and 13 of the 19 accounts reviewed would fall to $0 within 30 years. That work was done under the old $5,000 threshold, and raising the ceiling to $7,000 enlarges the pool of accounts that land there. All of this is permissive rather than mandatory, with most plans free to amend through December 31, 2026, so your Summary Plan Description governs your own account.

A prompt to sort your own accounts

Fill in the blanks and paste this into whichever assistant you use. It asks for arithmetic you can check against the IRS pages at the end, not a recommendation to trust.

I left a job and I have an old 401(k). Use 2026 federal rules, show every step.

- Balance $______ (pre-tax $______ / Roth $______), outstanding loan $______
- Age now ______, age during the calendar year I left that employer ______
- Employer stock in the account: yes / no, cost basis $______
- New employer's plan accepts rollovers in: yes / no / unknown
- I use a backdoor Roth: yes / no, existing traditional/SEP/SIMPLE IRAs $______
- Salary $______, filing status ______, state ______

Answer in order: whether the plan can force my balance out at the $1,000 and
$7,000 thresholds; whether the age-55 separation exception under IRC
72(t)(2)(A)(v) applies here and what rolling to an IRA would cost me; the Form
8606 pro-rata fraction if I roll into a traditional IRA; direct rollover versus a
check made out to me, including the 60-day shortfall; and the bracket-by-bracket
cost of cashing out. Flag any figure you are not sure is a 2026 value, and say
which answers depend on my plan document rather than on the tax code.

An answer you cannot trace to a bracket or a worksheet line is worth nothing here, the same rule that made sizing a quarterly estimated tax payment useful.

The $20,000 penalty and the $1,735 conversion bill are what push me toward moving an old 401(k) into the new employer's plan by default, and treating the IRA as a decision rather than a reflex. Neither of those costs announces itself while the transfer is going through.

Sources