401(k) Loans: What They Cost You in Growth

When money gets tight, the balance sitting in your retirement account can look like a solution. It is your money, after all. And unlike withdrawing it outright, a 401(k) loan lets you access cash without an immediate tax bill or penalty, as long as you play by the rules.

That framing is accurate, but incomplete. The mechanics of a 401(k) loan are more nuanced than a typical bank loan, and the real cost is not measured in interest paid. It is measured in the investment growth you never receive on the dollars that sat on the sidelines instead of working in your portfolio. For someone in their late 40s or 50s, that gap can be meaningful.

This article walks through how 401(k) loans actually work, what the IRS limits are, what happens if your employment situation changes mid-loan, and how to think honestly about the total cost. The goal is not to talk you out of it or into it, but to give you a clear picture so any decision you make is an informed one.

A 401(k) loan is not a withdrawal. When you borrow from your plan, you are taking cash out of your account temporarily, with a formal obligation to put it back. The IRS sets the guardrails, but your individual plan must also permit loans. Not every employer-sponsored plan does, so checking your plan documents or summary plan description is the logical first step.

Here is how the core mechanics work under IRS rules (see IRS Publication 560 and Internal Revenue Code Section 72(p)):

• Borrowing limit: Generally, you can borrow up to the lesser of $50,000 or 50% of your vested account balance. If your vested balance is $60,000, the ceiling is $30,000, not $50,000. The $50,000 cap is also reduced by the highest outstanding loan balance you have had in the prior 12 months, which matters if you have borrowed before.
• Repayment period: Most loans must be repaid within five years. The exception is a loan used to purchase your primary residence, which some plans allow to be repaid over a longer term.
• Repayment schedule: Payments are typically required at least quarterly, though most plans handle this through automatic payroll deductions, which keeps repayment straightforward.
• Interest rate: Your plan sets the rate, which is often the prime rate plus one percentage point. Critically, you pay that interest to yourself. It is deposited back into your account.
• No credit check: Because you are borrowing against your own balance, there is no credit inquiry and no impact on your credit score.

One detail worth understanding clearly: when the loan is originated, the plan liquidates investments in your account to fund it. Those dollars are no longer invested in the market. They are on loan to you. When you repay, contributions flow back into your account, but only gradually over the repayment term.

The interest-to-yourself feature sounds appealing, and it does reduce the sting compared to paying a bank. But it does not tell the whole story. The real cost of a 401(k) loan is the investment return the borrowed dollars would have earned if they had stayed invested.

Consider a hypothetical example for illustration purposes only. Suppose a 50-year-old borrows $30,000 from their 401(k) and repays it evenly over five years. During that period, let us assume the broader market generates an average annual return of 7%. The borrowed balance is not earning that 7% while it is on loan. The interest they pay back to themselves, say 8.5% (a hypothetical prime-plus-one rate), goes back into the account, but only as they repay. The average outstanding balance during repayment is roughly half the original loan, so the opportunity cost applies to a declining balance over time.

Running this through basic compounding, the foregone growth on that $30,000 over five years at 7% annually amounts to roughly $12,000 in missed gains on the full balance, though the actual figure depends on market returns, the repayment pace, and the specific loan structure. This is a simplified illustration, not a precise forecast.

There is also the double-taxation issue that financial educators frequently raise. You repay the loan with after-tax dollars. When you eventually withdraw that money in retirement, you pay income tax on it again. Traditional 401(k) contributions are pre-tax, so contributions and growth are taxed once, at withdrawal. Loan repayments, however, come from income that has already been taxed, so a portion of what you put back is effectively taxed twice. For Roth 401(k) balances, the calculation differs, since those contributions are already after-tax.

Finally, while repaying a loan, some people reduce their ongoing contributions to manage cash flow. If that means missing out on an employer match, that is an additional and immediate cost. Understanding how your employer match and vesting schedule work is relevant here, because reducing contributions during a loan repayment period can affect how much of your employer's contributions you ultimately retain.

This is the most consequential and frequently misunderstood aspect of 401(k) loans. If you leave your employer, whether voluntarily or not, while a loan is outstanding, the rules change fast.

Historically, the entire outstanding balance was due immediately upon separation, which created real hardship for people who were laid off. The Tax Cuts and Jobs Act of 2017 made the timeline more manageable. Under current rules, if you leave your job with an outstanding 401(k) loan, you generally have until the due date of your federal tax return for that year (including extensions) to repay the balance. For most people, that means until October 15 of the following year.

If you cannot repay within that window, the outstanding balance is treated as a taxable distribution. The IRS will add it to your ordinary income for the year, and if you are under 59½, a 10% early withdrawal penalty typically applies on top of that. On a $20,000 outstanding balance, someone in the 22% federal tax bracket under age 59½ could owe roughly $6,400 in combined federal taxes and penalty, before any state income taxes.

The practical risk is real. Job loss and financial hardship often coincide, which means the people most likely to need emergency funds are also the most vulnerable to this outcome. If your employment situation feels uncertain, this is a material factor to weigh. For a fuller look at what happens to your retirement savings when employment ends, this breakdown of 401(k) options after a job change covers the full picture.

None of the above means a 401(k) loan is never a reasonable option. It means it is a tool with a specific and narrow context where it can make sense relative to the alternatives.

Situations where some financial planners consider a 401(k) loan worth evaluating include:

• Avoiding high-interest debt: If the alternative is carrying a balance on a credit card at 20% or more, the opportunity cost of the 401(k) loan may be lower than the interest cost of the consumer debt, depending on how long the debt would otherwise remain outstanding.
• A genuine short-term bridge: If someone has a known, near-term cash event (a home sale closing, a bonus, an insurance settlement) and needs liquidity briefly, the five-year repayment structure may fit that situation.
• Job stability is high: The job-loss risk discussed above is far less concerning for someone in a stable position with decades at the same employer than for someone in a volatile industry or who is already considering a career change.

What a 401(k) loan is generally not well suited for is funding discretionary spending, covering ongoing living expenses, or bridging a structural gap between income and outgoings. Using retirement savings to paper over a cash flow problem that will persist after repayment begins can leave someone with both an ongoing shortfall and a loan payment.

It is also worth considering the full menu of alternatives: home equity lines of credit (if applicable), personal loans from a credit union, 0% introductory APR credit cards for short durations, or emergency funds. Each carries its own costs and risks, and a qualified financial adviser can help map those against your specific circumstances.

For context on how fees inside your plan affect your long-term balance, understanding what your 401(k) fees are really costing you adds another layer to the total-cost picture.

A 401(k) loan is not a financial trap, but it is also not free money. The mechanics are real: a defined borrowing ceiling, a five-year repayment clock, interest paid to yourself, and a job-change risk that can convert a manageable loan into an unexpected tax bill. The cost in foregone investment growth is genuine, even if it does not show up as a line item on your account statement.

Understanding those mechanics clearly puts you in a better position to decide whether this tool fits your situation or whether an alternative path makes more sense. Either way, the decision deserves more than a quick calculation of whether the monthly repayment fits the budget.

This article is for general informational and educational purposes only. It does not constitute personalised financial, tax, or legal advice. Every individual's financial situation is different. Please consult a qualified financial adviser, tax professional, or retirement plan specialist before making decisions about your 401(k) or any retirement account.