Changing Jobs? The Math of Your 401(k) Options

Job change weeks are chaotic, and the old 401(k) is the item most often decided by default — which usually means "left wherever it is, unopened, for years" or, worse, "cashed out to help with moving costs". Both defaults can be expensive. This guide walks through the four things you can do with a former employer's 401(k), with the actual arithmetic attached so the trade-offs are visible rather than vibes. Your plan's specific rules always govern; the numbers below are illustrations with stated assumptions.

The Four Options, in One Table

Three of the four keep the money invested and tax-sheltered. The rest of this guide is about choosing among those three — and about seeing the cost of the fourth clearly enough that it stays a non-option.

First: What Cashing Out Actually Costs

Worked example with assumptions stated: you leave a job at age 38 with a $60,000 401(k) balance and cash it out. You are under 59½, so this is an early distribution:

• Mandatory withholding: plans must withhold 20% for federal tax = $12,000. (This is a prepayment, not the final bill.)
• Early-distribution penalty: generally 10% of the distribution = $6,000.
• Income tax on top: the whole $60,000 is added to your year's taxable income. Assuming a 24% marginal federal rate, the final federal tax is about $14,400 — so at filing you owe roughly $2,400 beyond what was withheld, plus any state income tax.
• Total cost: about $20,400 federal (tax + penalty) before state tax. Of a $60,000 balance, roughly $39,600 reaches you.

That is the immediate bill. The larger cost is what the money would have done instead. At a 7% average annual return — an illustration assumption for a stock-heavy portfolio, not a prediction — $60,000 left invested for 25 years is:

$60,000 × 1.07²⁵ ≈ $325,000

Even scaling down for inflation to understand it in today's dollars at 3%, that is roughly $155,000 of present-day purchasing power, gone — in exchange for about $39,600 of spendable cash. There are true emergencies where a retirement account is the last resort; "between jobs" usually is not one. If money is genuinely tight during the transition, the honest comparison is against alternatives like a taxable withdrawal from savings or temporary income, not against the ~$20,400 haircut being optional. (Some narrow exceptions to the 10% penalty exist — substantially equal periodic payments, certain medical costs, and others — each with strict rules; treat them as research topics with a tax professional, not a default.)

Option by Option, With the Real Trade-Offs

Leave it in the old plan

Pros: nothing to do; the money stays invested; employer plans often carry institutional fund pricing, and creditor protection under federal ERISA law is strong. Cons: the account can be forgotten; annual fees may be higher than an IRA's; you can no longer add to it. One special rule to know before leaving money behind: the age-55 rule lets separated employees withdraw from that employer's 401(k) penalty-free from age 55 (versus 59½ elsewhere) — relevant for early retirees considering a future where they tap that specific account at 56.

Roll over to an IRA

Pros: typically the widest fund selection and lowest fees; everything in one place with one login and one asset allocation. Cons worth knowing: money in an IRA loses ERISA protection (state law protection for IRAs is generally meaningful but weaker and varies); the rule of 55 does not apply to IRA withdrawals; and if you ever use the backdoor Roth strategy, a pre-tax IRA balance triggers the pro-rata taxation rule that can make the maneuver costly. That last one surprises people — if backdoor Roth contributions are anywhere in your plan, rolling into an IRA needs a second look first.

Transfer to the new employer's plan

Pros: consolidates everything while keeping ERISA protections and (if the new plan allows and you are 55+) the age-55 rule for that plan; often one dashboard for household finances. Cons: you are limited to the new plan's fund menu and fee structure — check them before transferring; some plans also restrict transferring in until you have tenure there.

The order many planners sketch out

1. Compare fees and funds between the old plan, the new plan, and an IRA candidate — a 0.1% difference on $60,000 is $60/year compounding for decades (the mechanism is the same one described in our expense-ratio math).
2. Default to a rollover or transfer — keep the money sheltered and invested.
3. Use a direct (trustee-to-trustee) rollover, not a check to yourself. If the check route is used, the plan withholds 20% and you must deposit the full original amount within 60 days — including replacing the withheld 20% from your own pocket — or the shortfall is treated as a taxable distribution.
4. Do not sell the investments to "simplify" the move; most rollovers can move shares or simply change custodians without realizing taxes. Selling inside the account is not taxable, but it can put you out of the market during the transfer window — the timing risk described in our sequence-of-returns piece applies to career changers too.

The Two Mistakes That Do the Damage

• The automatic cash-out. Some plans send a check automatically for small balances (under ~$7,000 they can force you out; under ~$1,000 they may just mail a check) — respond to those letters rather than letting a 10% penalty arrive by mail.
• The 60-day window fumble. A personal-check rollover that misses 60 days becomes a full taxable distribution — tax plus penalty on everything. Direct rollovers make this failure impossible.

A job change is also the natural moment to revisit contribution strategy at the new employer — the free-money mechanics are covered in the employer match math, and if you are weighing plan types at the new job, the break-even arithmetic in Roth vs. traditional applies directly.

The 401(k) you leave behind took years of paychecks to build. Twenty minutes of paperwork is all it takes to move it somewhere it keeps working — and the only option that requires no paperwork at all is the one that costs five figures.