HELOC vs. 401(k) loan:
the hidden costs of each.

The 401(k) loan is sold with a tidy line: why pay interest to a bank when you can pay it to yourself? The framing is wrong. A 401(k) loan is a swap: your investment growth for a lower stated rate on the loan. Over any meaningful time horizon, the money you borrow out of the retirement account isn't earning what it would have earned if left alone, and the interest you pay yourself rarely makes up the difference.

A HELOC has problems of its own: variable rate, secured by your house, and vulnerable to being frozen when home values fall. It does not, however, tax your retirement wealth. For borrowers with real home equity and a job they expect to keep, the HELOC almost always wins the math once the forgone investment growth is priced in. The exceptions are real and worth naming. This page lays out both products, runs the true-cost math on a $40,000 need, and explains when each one fits.

The two loans, side by side

The two products look similar on the surface: both let you borrow against an asset you already own. The mechanics are different in almost every way that matters.

The “pay yourself interest” myth

The selling point is that the interest payment is a transfer from one pocket to another: your paycheck into your retirement account. The problem is that the money you borrow is no longer invested, and the interest you pay yourself is a substitute for the market returns you gave up, not a bonus on top of them.

Michael Kitces, an independent financial planner at Kitces.com, puts it plainly: “Paying 401(k) loan interest to yourself is really just contributing your own money to your own 401(k) account, without any growth at all.” When you borrow $40,000 out of your 401(k), that $40,000 is no longer in the market. The S&P 500 has averaged about 10% annual returns over the last century, including dividends reinvested. A 7.75% interest payment back to yourself replaces those returns with a smaller number on the same account.

Framed differently: the day before you borrow, your retirement dollars are earning 10% on average. The day after, they are earning 7.75% (because the borrowed portion is the loan you are paying to yourself, not stock). The gap, about 2.25 percentage points compounded over decades, is the hidden cost. It shows up in your retirement balance later, not on any loan statement.

A smaller second cost: the interest you pay yourself comes out of your paycheck, which is after-tax money. When you eventually withdraw that money in retirement, the interest portion is taxed again as ordinary income. On a $40,000 loan at 7.75% over 5 years, that is about $8,300 in interest, and the double taxation (assuming a 22% federal bracket in retirement) costs roughly $1,870.

The math, including the hidden cost

Two homeowners need $40,000 for a renovation over 5 years. Alex borrows from his 401(k); Dana takes a HELOC. Alex's loan statement shows a lower cost over the five years. His retirement balance at 65 shows the opposite.

Alex's 401(k) loan costs about $800 less in interest than Dana's HELOC over five years. That is the number loan officers and finance blogs tend to stop at. But Alex's retirement account has lost roughly $15,000 to $25,000 of growth it would have earned if left alone, and that gap never closes. Dana's retirement account is untouched. On the full wealth ledger, the HELOC is not marginally cheaper; it is cheaper by a multiple.

The job-loss tax bomb

The second large hidden cost is what happens if you leave the job while the loan is still outstanding. Under current rules, you have until the following year's tax deadline to repay the full balance. If you can't, the IRS treats the outstanding amount as a distribution from your 401(k), and for a borrower under 59½, that means federal income tax plus a 10% early-withdrawal penalty plus state income tax where applicable.

The Profit Sharing/401(k) Council of America estimates that, on a typical default by a participant under 59½, roughly 40 cents of every borrowed dollar goes to the government: 25% federal tax, 5% state tax, 10% penalty. On a $30,000 outstanding balance, that is about $12,000 in combined tax and penalty, plus the permanent loss of the $30,000 from retirement savings, plus every decade of compounding growth that $30,000 would have produced.

Job separation is the single most common cause of 401(k) loan defaults, and this is not a theoretical risk. The median tenure of an American worker at one employer is under five years, shorter than the standard five-year repayment term on a 401(k) loan. If your working life looks like the national average, there is meaningful probability that you will leave the job before the loan is paid off, whether by choice or not. A recurring question on personal-finance forums captures the moment: a borrower with an $11,000 loan outstanding, suddenly between jobs, deciding whether to take out another loan (credit card, personal loan, cash from savings) just to repay the 401(k) loan before the default deadline, or simply accept the tax bill and move on.

A HELOC has no equivalent. If you lose your job with a HELOC outstanding, the terms do not change. You still owe the money, and foreclosure is a possible outcome if you stop paying for months on end. But there is no 10% penalty, no immediate tax bill, and no sudden deadline forcing you to come up with $30,000 in cash. The worst-case HELOC outcome plays out over years; the worst-case 401(k)-loan outcome is triggered by a tax filing deadline.

Four things borrowers get wrong

1. The interest rate is almost irrelevant

The gap between a 7.02% HELOC and a 7.75% 401(k) loan is 0.75 percentage points, or roughly $150 a year in interest on a $40,000 balance. The opportunity cost on the same $40,000 at 10% historical returns is several thousand dollars a year. The opportunity cost, not the rate gap, should drive the decision.

2. Most borrowers stop contributing during repayment

401(k) loan repayments come out of the same paycheck that was funding retirement contributions. In practice, many borrowers reduce or suspend contributions during the repayment period to absorb the loan payment. If your employer matches the first 6% of salary and you stop contributing, you've forfeited that match for every year the loan is outstanding. On a $100,000 salary with a 3% match (50% on the first 6%), that's $3,000 a year — another $15,000 over a 5-year loan you may not have counted.

3. A 401(k) loan default permanently reduces your retirement

If the loan defaults (most commonly at job separation), you cannot repay it back into the 401(k) after the grace period. You cannot roll the amount back in. You cannot undo the taxable distribution. The money is gone from your retirement account, and the taxes and penalties are gone from your bank account. The effect compounds over decades: at age 30, a $30,000 loan default doesn't just cost you $30,000 now plus $12,000 in taxes. It costs the roughly $500,000 to $800,000 that $30,000 would have grown into by age 65 at long-run market returns of 8%–10%.

4. “No credit check” is a real advantage for some borrowers

One advantage of a 401(k) loan is not a myth: you don't need a credit score to qualify. If your credit has been damaged by medical debt, a recent divorce, or a bankruptcy, a HELOC may be unavailable or available only at punishing rates. A 401(k) loan bypasses that. It is also faster to fund than a HELOC (1–2 weeks vs. 2–6) and has no collateral on your home. For credit-damaged borrowers with short-term needs, the 401(k) loan is sometimes the only reasonable option. This article argues it is usually not the better one. It does not argue it is always wrong.

Which product wins, and for whom

Two conditions have to line up before a 401(k) loan is the right answer: you can't get a HELOC (or the HELOC numbers are materially worse), and the need is urgent enough to outweigh the opportunity cost. Both are rare.

A third case is worth naming. If you have real home equity and stable income, the honest answer is to avoid both products if you can. Both trade something durable for a temporary need, and the math above rarely makes either look like a good move in absolute terms, only relative to the other.

When neither is right

A borrowing decision is already losing ground if one of these applies. The right move is to fix the underlying problem, not to choose between two ways of financing it.

• The purpose is discretionary. A vacation, a wedding, a car upgrade. Neither your house nor your retirement account should fund a short-term want; the interest compounds for decades after the purchase is used up.
• You are already carrying substantial debt. Adding a HELOC or 401(k) loan on top of existing credit card balances, student loans, or auto loans doesn't fix the debt; it reshuffles it. Until the underlying spending or income issue is addressed, every new loan only delays the problem.
• Your income is unstable. Both products assume you can make the payment every month until the loan is retired. The 401(k) loan adds the job-loss tax-bomb risk on top. If you can't confidently answer "yes" to "can I make this payment for five years?" the answer to "which loan?" is neither.
• A 0% balance-transfer card or personal savings would work. For amounts under ~$15,000 with a clear 12–18-month payoff, a promotional balance transfer (for the disciplined) or a real emergency fund beats either structured loan on every dimension.
• You are within a few years of retirement. A HELOC's variable rate paired with a fixed retirement income is dangerous, and a 401(k) loan shortens an already-short compounding horizon. Consider a fixed-rate home equity loan instead, or not borrowing at all.

The decision, in one paragraph

The 401(k) loan looks cheaper on the brochure and usually isn't. The interest rate sits a fraction of a point below a HELOC's, but the money you borrow is no longer earning the 10% your retirement account would otherwise average. Over five years on a $40,000 loan, that gap is $15,000 to $25,000 of retirement wealth that doesn't come back. Add the job-loss tax bomb (40% of the balance to the government if you default before 59½) and the 401(k) loan becomes the expensive choice for almost anyone with a job and some home equity. The exceptions are real: damaged credit that disqualifies you from a HELOC, a very short-term need, an unusually stable job. Outside those narrow cases, the HELOC is almost always the cheaper loan once you count what it leaves untouched.