On paper, a 401(k) loan looks like the cheapest money you can get. No credit check, an interest rate near prime, and the kicker every HR pamphlet mentions: you pay the interest to yourself. When a roof fails or a medical bill lands, borrowing from your own retirement account can feel less like debt and more like moving money between pockets.
The pamphlet version is not wrong, but it is incomplete. The rules that govern plan loans carry deadlines and penalties that can turn a tidy loan into a taxable distribution, and the quietest cost, the growth your money never earns while it is out of the account, does not appear on any statement. Here is the full price tag.
What the rules actually allow
Federal law caps a plan loan at the lesser of $50,000 or half of your vested account balance, with a small exception that lets you borrow up to $10,000 even if that is more than half, as the IRS explains in its plan loan rules. Your employer’s plan can be stricter, and not every plan offers loans at all; the plan document controls.
Repayment is standardized too. The loan generally must be repaid within five years through substantially level payments made at least quarterly, in practice usually by payroll deduction. One exception: a loan used to buy your main home can run longer. Miss the payment schedule and the consequences are not late fees; they are taxes, which is where borrowers get hurt.
“Paying interest to yourself” is half true
The interest on a 401(k) loan does land in your own account, which genuinely beats paying it to a bank. But notice what the arrangement replaces. The dollars you borrowed were invested; while they are out on loan to you, they earn your loan’s interest rate instead of whatever the market returns. In strong market years, that gap is the loan’s largest cost, and it is invisible. The IRS makes the same point bluntly in its guidance on considering a 401(k) loan: you give up some or all of the investment growth the borrowed money would have produced.
There is also a smaller wrinkle: you repay the loan, including its interest, with money that has already been taxed, and those same dollars will be taxed again when withdrawn in retirement. And some borrowers trim their regular contributions while repaying, sometimes below the employer match, which converts a cheap loan into a genuinely expensive one. If you borrow, keep contributing at least enough to collect the full match.
The default trap: when a loan becomes a distribution
Fail to make the required payments and the plan will declare the outstanding balance a deemed distribution. At that point the unpaid amount becomes taxable income, and if you are under 59 and a half, it generally also triggers the 10 percent additional tax on early distributions described in IRS Tax Topic 558. A $20,000 defaulted loan for someone in the 22 percent bracket can mean roughly $6,400 in combined federal income tax and penalty, plus any state tax, on money that is already spent.
Plans may offer a cure period, often through the end of the quarter after the missed payment, to catch up before default. If your paycheck deductions ever stop, because of a leave of absence, a payroll error, or anything else, treat it as urgent and call the plan.
The job-change problem
The riskiest moment for a 401(k) borrower is a resignation letter or a layoff notice. Many plans require the loan to be repaid in full shortly after you leave; if it is not, the plan offsets your balance by the unpaid amount, and that offset is treated as a distribution, taxable and potentially penalized just like a default.
The law does provide a longer runway than it used to. For a loan offset caused by leaving your job or by plan termination, you have until the due date of your federal tax return for that year, including extensions, to come up with the money and roll the offset amount into an IRA or new employer’s plan, which erases the tax bill. That is real breathing room, but it still requires replacing the cash from somewhere. Anyone considering a plan loan should price this scenario honestly: how would you repay the balance if your job ended six months from now?
When the loan makes sense anyway
None of this makes 401(k) loans categorically bad. Compared with a 25 percent credit card balance or a payday-style product, a plan loan is often the least expensive option available, especially for a short-term, clearly repayable need. It can also be reasonable as a bridge in a home purchase, where the longer repayment term applies.
The honest checklist looks like this. The purpose is a real need, not routine spending. The amount leaves your retirement trajectory intact. Your job is reasonably secure, and you could handle the offset rules if it turned out not to be. You will keep contributing through the payback period. And you have compared the true alternatives, including a temporary savings drawdown, a home equity line, or, for genuine emergencies, the penalty exceptions and hardship provisions your plan may offer.
Borrowing from your future self is sometimes the right call. Just read the loan paperwork the way the IRS does: as a transaction with a five-year clock, a tax bomb attached to nonpayment, and a price that includes everything your money would have become if you had left it alone.
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