A woman is 50, has $300,000 in her 401(k), and wants to renovate her kitchen. Her plan looks tidy on paper: borrow $50,000 from the plan, pay it back over five years at 7% via payroll deduction, and pay the interest back to herself. No bank, no credit check, no problem. I would tell her to walk away from that loan. The reason has almost nothing to do with the 7% rate.
The real cost is closer to $100,000 of retirement balance she will never see, and it shows up in two places most borrowers never run the math on.
The principal that stops working for five years
When that $50,000 leaves the account, it stops compounding inside the 401(k). The interest she pays herself sounds like a workaround, but it is paid with after-tax dollars and then taxed again as ordinary income when she withdraws it in retirement. That is the double-tax quirk of 401(k) loan interest that almost no plan participant has explained to them.
The opportunity cost is the bigger number. $50,000 left invested for 15 years at a 7% growth assumption compounds to roughly $138,000 by age 65. The same $50,000, repaid by year five and then invested for the remaining 10 years, lands closer to $98,000. That gap is about $40,000, and it exists even if Sarah does everything else right.
For context on what a 7% assumption means, the S&P 500 returned 30% over the past year and 255% over the past decade through the SPDR S&P 500 ETF Trust (NYSEARCA:SPY | SPY Price Prediction). Long-run averages are lower, but pulling $50,000 out of equities for five years of a strong cycle is an expensive way to fund a kitchen.
The match she stops earning while paying herself back
The quieter damage is the contribution pause. Most borrowers cannot fit the loan repayment and full salary deferrals into the same monthly cash flow, so they cut contributions and forfeit the employer match. A $5,000 annual match missed from age 50 through 54, compounded at 7% to age 65, is roughly another $60,000 of forgone balance. Each year’s missed deposit grows for a different horizon, and the earliest one matters most.
Add the two together and the loan that felt free costs Sarah about $100,000 of retirement balance at 65. That is real money, and it lands precisely when she has the least time to recover it.
The job-loss trapdoor nobody warns you about
There is a third risk that is binary rather than mathematical. If Sarah leaves her employer or is terminated before the loan is fully repaid, the outstanding balance is treated as a deemed distribution. The full amount becomes taxable as ordinary income, and the 10% early withdrawal penalty applies if she is under 59.5. On a $35,000 outstanding balance, that can mean a five-figure tax bill due in the same year she just lost her income.
The macro backdrop does not help either. University of Michigan consumer sentiment sits at 53.3, in pessimistic territory, and the national savings rate has fallen from 6.2% to 4.0% over two years. Layoffs in a soft cycle are exactly when deemed distributions hit hardest.
What I would do instead
- Price a HELOC or 0% promotional credit first. With the 10-year Treasury near 4.4% and the Fed funds upper bound near 3.8%, home equity rates are not cheap, but the interest is potentially deductible if the renovation qualifies, and the principal stays invested. A 0% promotional card on a smaller scope of work can bridge 12 to 18 months without touching the 401(k).
- If you take the loan anyway, do not cut contributions. Run the household budget so payroll deferrals stay at the level that captures the full employer match. Losing the match is what turns a $40,000 mistake into a $100,000 one.
- Treat the 401(k) loan as the last option, not the easy one. Anchor the decision to the deemed-distribution risk: if there is any realistic chance of a job change in the next five years, the loan is the wrong tool.
If the renovation budget is tight enough that a 401(k) loan looks attractive, that is usually the signal to shrink the project, not the retirement account. With inflation still running above the Fed’s 2% target, the dollars Sarah pulls out today are also worth less by the time she pays them back. Compare quotes from a fee-only advisor through SmartAsset before signing the paperwork. The hour of math is cheaper than the $100,000.
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