TSP loans: when they make sense (and when they don't)

The TSP loan is one of the most misunderstood tools in the plan. On the surface it looks free: you borrow from your own balance, pay yourself back with interest, and the rate is low. In reality it sits somewhere between 'occasionally sensible' and 'quietly expensive,' and the difference depends entirely on why you're borrowing and what you give up while the money is out of the market. Before you take one, it helps to see exactly what the loan costs beyond the interest rate.

How a TSP loan works

You can borrow from your own contributions and their earnings - a general-purpose loan repaid over up to five years, or a residential loan for a primary home repaid over up to fifteen. The interest rate is tied to the G Fund rate at the time you take it, and here's the part that sounds appealing: the interest you pay goes back into your own account, not to a bank. Repayment comes out of your pay automatically. There are minimum and maximum loan amounts, and a small processing fee.

The cost that isn't the interest rate

The real price of a TSP loan is opportunity cost. Every dollar you pull out stops being invested - so if the market returns 8% while your money sits in loan limbo earning the G Fund rate, the gap is your true cost, and it can dwarf the interest. Borrow $15,000 during a strong market year and the foregone growth can run into the thousands. You also repay with after-tax dollars that will be taxed again at withdrawal in a traditional account, a subtle form of double taxation on the interest portion.

When it can actually make sense

• Avoiding a genuinely worse debt: replacing a 25% credit card or a title loan with a low-rate TSP loan can be a rational bridge - if you kill the habit that created the balance.
• A residential loan toward a primary-home down payment, where the 15-year term and low rate compare well to other borrowing.
• A short, definite need you'll repay fast, where the time out of the market is measured in months, not years.

When to walk away

• You have an emergency fund - use it; that's what it's for, and it costs nothing in foregone growth.
• You're funding a want (a truck, a vacation, a wedding upgrade) - borrowing from retirement for lifestyle is exactly backward.
• You might separate before repaying - the taxable-distribution risk makes it a gamble against your own career timeline.

The bottom line

A TSP loan is cheaper than any storefront lender and repays interest to yourself, but its real cost is the market growth you forfeit while the money is out, plus a genuine tax trap if you separate before repaying. Reach for your emergency fund first, use a TSP loan only to escape genuinely worse debt or bridge a short, definite need - never to fund a want - and never take one if separation might arrive before the balance is gone.