The Real Cost of a TSP Loan (And Why I've Never Taken One)

Since I enlisted in January, I've had more soldiers ask me about TSP loans than almost anything else. Car needs work. Leave got expensive. A buddy's flying in a bad direction financially and needs help. The TSP loan sits right there in your account, feels like your own money, and the paperwork takes twenty minutes. So people take it.

I never have. Not once in eight years of investing. Here's the math that keeps me out of it.

It Feels Free. It Isn't.

The pitch sounds harmless: you borrow from your own TSP balance, and you pay yourself back the interest instead of a bank. On paper, that looks like a wash. In practice, it's not — because the money you pull out stops being invested the moment it leaves the fund. It's not earning market returns anymore. It's just sitting there as a loan balance you owe yourself, at G Fund-adjusted interest, while the money that would have replaced it stays out of the C Fund entirely.

Say you pull $15,000 out to cover a car repair and some leave travel. You repay it over four years through payroll deduction, like most soldiers do. That $15,000 is now off the table for growth the entire time. If it had stayed in the C Fund and grown at even a conservative long-run average, you'd be looking at roughly $21,000-$22,000 by the time the loan is repaid. Instead you have $15,000 back, plus whatever modest interest you paid yourself. The gap — six or seven thousand dollars — didn't go to a bank. It just never got made.

The Part Nobody Explains at the Briefing

The bigger risk isn't the math above. It's what happens if you separate, get out, or change duty stations and miss a repayment window. An unpaid TSP loan balance gets converted into a taxable distribution. That means it counts as income the year it happens, you owe tax on it, and if you're under 59½ you likely owe a 10% early withdrawal penalty on top. A loan you took to solve a short-term cash problem can turn into a tax bill that creates a bigger one.

I've watched this blindside soldiers who took a loan with every intention of paying it back on schedule, then got orders, a med board, or a separation that didn't line up with the repayment plan. The TSP doesn't care about your timeline. It cares about the note.

What I Do Instead

I keep a separate cash reserve outside my investments for exactly this kind of expense — car repairs, unexpected leave costs, the stuff that isn't a true emergency but isn't nothing either. That reserve gets built the same way everything else in my plan gets built: automatically, before I have a chance to spend it, and completely separate from anything invested in the market. If the number in that account gets low, I know it before the car breaks down, not after.

That's the whole approach, and it's not complicated on purpose. The TSP is for compounding, untouched, for decades. A checking or savings buffer is for life. When you keep those two buckets separate, you never have to choose between fixing your car and stealing from your own retirement to do it.

Do the Math Before You Sign

If you're staring at a TSP loan form right now, run the numbers first. Figure out what that money would likely grow into if you left it alone for the life of the loan. Compare that to what you'll actually save in interest by borrowing from yourself instead of a bank or a 0% card. Most of the time, the loan loses that comparison badly — you're just paying a hidden cost that never shows up on a statement.

I built a $781,000 net worth by treating my TSP and my index funds as money I don't touch, under any circumstance, for any reason short of true emergency. Boring on purpose, relentless by design. A TSP loan breaks that rule quietly, and quiet rule-breaking is how most people's retirement accounts end up smaller than they should be. Leave it invested. Build the cash reserve instead. Your future self is the one paying for the decision either way — make sure you're paying them back, not stealing from them.