Borrowing from your 401(k): the real tradeoffs of a plan loan

A 401(k) loan is one of the most misunderstood moves in personal finance — pitched as 'borrowing from yourself and paying yourself the interest,' which sounds like a free lunch. Sometimes it's a reasonable tool; often it's a costlier choice than it appears. Most plans let you borrow up to 50% of your vested balance, capped around $50,000, repaid with interest over up to five years (longer for a home purchase) through payroll deductions. The catch isn't the interest rate — it's the opportunity cost and a job-loss trap that can convert the loan into a taxable disaster.

How a 401(k) loan actually works

You borrow from your own balance, and the interest you pay goes back into your account rather than to a bank. There's no credit check and no impact on your credit score, and the rate is usually modest (often the prime rate plus a point or two). Repayment comes out of your paycheck automatically. On the surface, paying interest to yourself sounds strictly better than paying a lender. The problems are subtler.

The real costs people miss

• Opportunity cost: the borrowed money is out of the market. If your investments would have earned 8% while your loan 'pays you' 6%, you've lost the difference on the borrowed amount for the whole loan term — and missed compounding you never get back.
• Double taxation on the interest: you repay the loan with after-tax dollars, and that money is taxed again when you withdraw it in retirement. The interest portion effectively gets taxed twice.
• Reduced contributions: many people cut or pause their regular contributions while repaying a loan, sometimes forfeiting employer match — often the biggest hidden cost of all.
• It's still your retirement: raiding it for a want (not a genuine need) trades future security for present convenience.

When a 401(k) loan can make sense

• As a short-term bridge you're confident you can repay quickly, while your job is stable — e.g., covering a gap before a known inflow.
• To avoid a genuinely worse option, like a high-interest payday loan or credit-card debt at 24%, when no cheaper borrowing is available.
• For a true emergency where the alternatives are all worse, and you'll keep contributing enough to capture the full match.
• Never for discretionary wants, and never if there's meaningful risk you'll leave the job before repaying.

The bottom line

A 401(k) loan isn't automatically a mistake, but it's rarely the bargain it's sold as. The interest going to yourself is real, but so are the lost market growth, the double-taxed interest, the contributions and match people quietly drop, and above all the job-loss trap that can turn the balance into a taxed, penalized distribution overnight. Reserve it for short-term bridges or genuinely worse alternatives, keep your contributions and match intact, and never borrow against your retirement for something you merely want. When in doubt, price the alternatives first.