A 401(k) loan works differently from a traditional bank loan because you borrow from your retirement plan account and repay the loan, including interest, back to that account. The IRS explains this in its guidance on loans from 401(k) plans.

So, who gets the interest on a 401(k) loan? The interest is credited back to your retirement account rather than paid to a bank or other outside lender.

That feature is one reason 401(k) loans can sound appealing. But the interest rate is only one part of the decision. Borrowing can also affect how much of your retirement money remains invested, and leaving your employer with a loan outstanding can create additional repayment and tax considerations.

What Interest Rate Does a 401(k) Loan Charge?

There is no single interest rate that applies to every 401(k) loan. Your plan determines the rate and other loan terms.

Federal regulations generally assume that a qualifying plan loan has an interest rate and repayment terms that are commercially reasonable, but the regulations do not establish one universal “prime plus 1%” or “prime plus 2%” formula for every plan. See 26 CFR § 1.72(p)-1.

That means the most useful place to find your actual rate is your plan’s loan documents or summary plan description.

Federal rules also limit how much can generally be borrowed. The maximum is typically based on the lesser of a federal dollar limit or a percentage of your vested account balance, and previous or outstanding plan loans can reduce the amount available. A plan may also impose stricter limits or choose not to offer loans at all. The IRS discusses these limits in its guidance on borrowing limits for participants with multiple plan loans.

In general, a qualifying loan must be repaid within five years. A longer repayment period may be permitted when the loan is used to acquire your principal residence.

Where Does the Interest on a 401(k) Loan Go?

The interest you pay on a 401(k) loan goes back into your retirement account along with the principal repayments.

Compared with a traditional loan, that can sound like an obvious advantage because the interest is not being paid to an outside lender.

There is still an important tradeoff: the money borrowed from the plan is no longer invested in the same investments it held before the loan. That can create an opportunity cost if those investments rise while the loan is outstanding.

For example, suppose $20,000 that otherwise would have remained invested would have earned 8% annually for two years. Mathematically, $20,000 growing at a steady 8% for two years would increase to about $23,328.

That does not mean a borrower automatically “loses” $3,328. Market returns are uncertain, and investments can fall as well as rise. The point is that a 401(k) loan changes what that portion of the account is exposed to while the loan is being repaid.

The interest credited back to the account provides some return, but it does not guarantee the same result the original investments would have produced.

How Does 401(k) Loan Repayment Actually Work?

Many plans arrange 401(k) loan repayments through payroll deductions, but the specific payment process depends on the plan.

To satisfy the federal loan rules, repayments generally must be made in substantially level installments of principal and interest at least quarterly over the required repayment period.

Payroll deductions can make repayment easier to manage, but they do not eliminate the consequences of missed or discontinued payments. If a loan no longer meets the repayment requirements, the unpaid amount may be treated as a taxable plan distribution.

401(k) loans also differ from conventional consumer loans because eligibility comes through the retirement plan rather than a traditional loan application. Whether your plan permits a loan, how much you can borrow, and the loan’s terms are determined by the plan and applicable federal rules.

That can make a 401(k) loan look attractive when compared with high-interest debt. But comparing the stated interest rates alone can miss the effect on retirement savings and the potential consequences if repayment does not go as planned.

Is the Interest on a 401(k) Loan Taxed Twice?

This question needs more context than a simple yes or no.

Loan repayments generally come from money you receive after payroll taxes and income-tax withholding, just as repayments on many other types of loans do. The original 401(k) loan itself is generally not taxable when it meets the federal loan requirements and is repaid according to its terms. The IRS discusses these rules in its guidance on hardships, early withdrawals, and loans.

For a traditional 401(k), distributions of previously untaxed contributions and earnings are generally included in taxable income when withdrawn.

Because the interest portion of a loan payment is made with after-tax dollars and credited back into the traditional 401(k), people sometimes describe that interest as being “taxed twice”: once when the money used to make the payment is earned and again when taxable money is eventually distributed from the account.

That shorthand can be misleading, though. The first tax is the normal income tax on the wages used to make the repayment, not a special second tax imposed because you took a 401(k) loan.

It’s also important not to apply the same explanation automatically to every account. Roth 401(k) contributions and qualified Roth distributions have different tax treatment.

So the tax treatment of the interest can be a consideration, but it should not be described as a universal extra tax or a fixed cost of every 401(k) loan.

What Happens to a 401(k) Loan If You Leave Your Job?

Leaving or losing your job does not create one universal repayment deadline for every 401(k) loan.

The IRS notes that a plan may require a participant to repay an outstanding loan in full after leaving the employer. What happens next depends on the plan and how the outstanding balance is handled.

If the plan offsets an outstanding loan balance because of separation from employment, the offset may qualify for special rollover treatment. A qualified plan loan offset can generally be rolled over by the due date, including extensions, for the federal income tax return for the year in which the offset occurs. See IRS Tax Topic 413.

That tax-return deadline is a rollover deadline, however. It should not be confused with a promise that every plan lets participants continue making normal loan payments until their tax return is due.

If an unpaid amount becomes a taxable distribution, previously untaxed amounts generally must be included in income. An additional 10% early-distribution tax may also apply unless the participant is at least age 59½ or qualifies for another exception.

That makes a possible job change an important factor to review before taking a plan loan.

So, Is a 401(k) Loan Worth It?

A 401(k) loan can have features that look attractive compared with other borrowing options. The interest is repaid to your account, and the loan terms may differ significantly from those available through conventional lenders.

But that does not automatically make it the least expensive or most appropriate choice.

Before borrowing, it can help to compare:

• The 401(k) loan’s interest rate and any fees
• The cost of other borrowing options
• How much retirement money would no longer be invested
• How secure your current employment situation is
• What the plan requires if you leave your job
• Whether the loan payment fits your budget
• How borrowing could affect your longer-term retirement savings

The key question is not simply, “Do I pay the interest to myself?” The more useful question is whether the overall borrowing arrangement makes sense once the repayment terms, retirement impact, and potential tax consequences are considered together.