A TSP loan is a kind of borrowing where the interest goes back into your own retirement account instead of a bank’s. That makes it cheap — 4.500% as of July 2026, versus 20.94% on a credit card — but not free, because the money you borrow stops “earning” while it’s not invested in your TSP account. This calculator shows you both halves of that trade.
Start with the five input fields below and you’ll know your monthly payment in a few seconds. If you want to see what the loan might really cost your retirement — across thousands of possible market futures instead of one hopeful guess — switch on Full detail and keep going 😎
Change anything and every figure below updates.
You can only borrow against your own contributions and their earnings — subtract all agency matches!
A TSP loan can only draw on your own TSP contributions and their earnings. Agency money, and anything in the Mutual Fund Window, is off limits.
Used for the opportunity-cost projection. Your contributions and the agency match keep running while a TSP loan is outstanding, so they appear in both scenarios.
Determines what the borrowed money would have earned if it had remained in your TSP account instead. The simulation uses the real monthly history of this fund allocation — add the S or I Fund and it can only reach back to their May 2001 start.
Out of every paycheck
A single assumed return is a thin answer to a question this uncertain. This simulation runs your scenario through thousands of possible futures, each one stitched together from real TSP fund returns — including the stretches where the market went nowhere for years. Watch the line in the middle (the median outcome); an amount below zero is a future where taking the loan left you better off.
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What you type here is yours. We save it only so that this page remembers your numbers. We never sell or share this information, and we don’t ask for your name, Social Security number or TSP login. Nothing here touches your actual TSP account.
Every number above comes from the current TSP rules. Here’s what’s baked in:
The TSP applies three tests and gives you the smallest answer. The calculator runs all three and tells you which one is holding you back:
The floor is $1,000, and you need at least that much of your own money in the account to borrow at all. General purpose loans run 12–60 months and need no documentation; primary residence loans run 61–180 months and require paperwork within 30 days. You can have two loans outstanding at once, only one of which may be a residence loan.
Am I really paying interest to myself?
Yes. Every payment, principal and interest, lands in your own TSP account. The only money that leaves for good is the one-time processing fee. That’s a genuinely better deal than any consumer lender offers — and it’s also why the sticker rate isn’t the whole story.
So what’s the catch?
The borrowed money isn’t invested while it’s out. If your TSP fund portfolio returns more than your loan rate over those years, you end up behind; if it returns less, you end up ahead. Nobody knows which in advance, which is why our simulation shows you a range instead of a single number.
Does a TSP loan affect my credit?
No. There’s no credit check to get one, and it doesn’t appear on your credit report.
What if I leave federal service before it’s repaid?
This is the risk worth taking seriously. The balance has to be repaid by the deadline or it becomes a taxed distribution — ordinary income tax, plus a 10% early-withdrawal penalty if you’re under 59½. You can avoid the tax hit by rolling an equivalent amount of your own money into an IRA or another eligible plan by your filing deadline.
Can I refinance if rates drop?
There’s no refinancing in the TSP. To get a different rate you’d repay the loan in full, wait 30 business days, and apply again — and the new loan amount would still be capped by that 12-month highest-balance test.
Is a loan better than a hardship withdrawal?
Almost always, if you qualify for both. A withdrawal is permanent, taxed, and possibly penalized; a loan puts the money back.
The short version: we resample real TSP fund history in chunks, run your actual loan and TSP portfolio parameters (as entered in the calculator inputs) through 2,000 of the futures that produces, and report the whole distribution instead of a single number. It is a Monte Carlo simulation — thousands of random trials, summarized by their spread — of the nonparametric kind, where the randomness is drawn from stock and bond market history itself rather than from a curve fitted to it.
The data. Monthly total returns for the five core TSP funds, computed from month-end share prices.
The window depends on your allocation. Every fund is pinned to its official inception date — G in April 1987, F and C in January 1988, S and I in May 2001 — and a simulation uses the longest stretch in which every fund you actually hold has real data. A G/F/C mix therefore draws on history back to January 1988, which includes the dot-com bust, 2008 and 2022. If you add an allocation in the S or I Fund, the window starts in May 2001 instead.
The portfolio allocation is applied before the resampling, not after. We combine the five funds into one portfolio return series using the allocation percentages, rebalanced monthly, and resample that. Every drawn month then carries the cross-fund relationship of that specific calendar month — the actual month stocks and bonds fell together — rather than a correlation we invented and imposed on them.
The sampling method is a stationary block bootstrap (Politis & Romano, 1994). Each of the 2,000 futures is stitched together from randomly chosen runs of consecutive historical months, with run lengths averaging twelve months.
What runs down each path. Two accounts, side by side, receiving exactly the same drawn returns: one where you took the loan (starting lower by the amount borrowed) and one where you did not. Your ongoing contributions land in both. Your loan repayments land only in the first — and they land monthly, compounding from the month you make them rather than sitting idle until payoff. Money you have already repaid is back in the market earning for the rest of the term. The gap between the two accounts at payoff is what the loan cost you on that path.
Reading the output. Sort the 2,000 final figures and read the percentiles off, interpolating between neighboring paths: the median is the middle, and the 5th and 95th are the two tails quoted above the chart. The “left your account better off” percentage is the share of the 2,000 that finished below zero. The bold median line is the per-point median across all 2,000 paths. The chart draws 80 of the paths.
The same inputs always give you the same chart. The random seed is derived from the inputs that actually move the answer: amount, term, rate, allocation and loan type. It deliberately ignores your balance, salary and contribution percentages, because those are added to both accounts and cancel out of the difference between them. Reload with the same loan and you get the same picture.
What it does not model. Everything is nominal — no inflation adjustment. No taxes, no pay raises, and no change to your allocation over the life of the loan. And no separation from federal service before the loan is repaid, which is a risk in a TSP loan and not something a return simulation can speak to.
TSP loan rules, fees, terms, and the 2026 contribution limits are from official tsp.gov publications. The TSP loan interest rate is the previous month’s G Fund interest rate we publish daily on this website. The simulation resamples the actual monthly total returns of the TSP core funds, which we’ve tracked since the plan’s early days.
Read more about the current TSP loan interest rate — today’s rate, its full history, and how it compares to what banks charge.
This calculator is provided for general educational and informational purposes only. It is not financial, investment, tax, legal or accounting advice, and it is not a recommendation to take or to avoid a TSP loan.
TSP Folio is not a registered investment adviser, broker-dealer, financial planner, attorney or certified public accountant, and nothing here creates an advisory or fiduciary relationship of any kind. We are not affiliated with, endorsed by, or acting on behalf of the Thrift Savings Plan, the Federal Retirement Thrift Investment Board, or any agency of the United States government.
The results are estimates produced from the figures you enter and from published TSP rules as we understand them at the time of writing. Plan rules, IRS limits, fees and interest rates change. Your agency, your payroll office and the TSP itself may compute your actual loan amount, payment, eligibility and payoff date differently, and their figures — not ours — are the ones that govern. Always confirm anything that matters at tsp.gov before you act on it.
The simulation is a statistical model built from historical fund returns. Past performance does not predict future results, historical patterns need not repeat, and no outcome shown here is promised, guaranteed or even likely to occur exactly as displayed. The range of outcomes is not exhaustive: real markets can and do fall outside anything a model produces from the past.
We believe these calculations to be accurate, but we provide them without warranty of any kind, express or implied, including any implied warranty of merchantability or fitness for a particular purpose. To the fullest extent permitted by law, TSP Folio and its operators accept no liability for any loss or damage of any kind arising from the use of, or reliance on, this calculator.
Borrowing against your retirement savings is a consequential decision with long-lasting effects. If you are not fully comfortable making this decision on your own, please consult a qualified financial adviser, tax professional or attorney about your specific circumstances before you act.