TSP Loan Impact Calculator
Calculate your TSP loan payment and — uniquely — what the borrowed principal would have grown to if left invested. See the real cost of borrowing from your retirement account.
The differentiator no competitor offers
Any purpose. No documentation required. Term: 1–5 years.
Default: 4.500% (June 2026). Rate fixed at application for the loan's full term.
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How the loan math works
TSP loans use standard amortization — each payment covers accruing interest first, then reduces principal. The critical detail: the loan fee ($50 for general purpose, $100 for residential) is deducted from the disbursed proceeds, but amortization runs on the full requested principal.
At 4.500% / 26 periods = 0.1731% per biweekly period. Over 130 periods (5 years), a $20,000 loan produces a biweekly payment of $171.93, total repaid $22,350.90, and interest to self of $2,350.90.
2026 G Fund rates — month by month
The loan rate is fixed to the G Fund rate for the month before your loan request. It stays fixed for the life of the loan regardless of subsequent G Fund changes.
| Month | G Fund Rate |
|---|---|
| January 2026 | 4.250% |
| February 2026 | 4.250% |
| March 2026 | 4.000% |
| April 2026 | 4.375% |
| May 2026 | 4.500% |
| June 2026 | 4.500% |
General purpose vs residential loan
Two loan types — same interest rate formula, different fee and term limits.
| Feature | General Purpose | Residential |
|---|---|---|
| Purpose | Any reason | Primary home purchase/construction |
| Term range | 1–5 years (12–60 months) | Up to 15 years (up to 180 months) |
| Loan fee | $50 (deducted from proceeds) | $100 (deducted from proceeds) |
| Documentation | None required | Required (purchase agreement / construction docs) |
The real cost: opportunity cost explained
When you borrow from TSP, the principal leaves your investment funds (C, S, I, F) and earns 0% market return while it's outstanding. Meanwhile you repay it — plus interest — rebuilding the balance. The question the standard loan calculator skips: what would that principal have grown to if you had left it invested?
This calculator uses Approach A (lump-sum modeling): it treats the full borrowed principal as if it had remained invested for the entire loan term. This modestly overstates the opportunity cost because in practice your repayments gradually rebuild the balance — but it is the more conservative and intuitive framing. The disclosure label in the results makes this explicit.
The interest you pay yourself partially compensates for the removed principal — you earn the G Fund rate on repayments flowing back into your account. But the net gap (the difference between what the market would have returned and what the G Fund interest returns) is the honest measure of what borrowing costs your retirement.
TSP loan rules: maximums, limits, and the two-loan rule
The maximum TSP loan is the smallest of three calculations (5 CFR § 1655.6(b)):
- Your vested account balance attributable to employee contributions and earnings, excluding outstanding loan principal.
- The greater of 50% of your vested balance or $10,000, then subtract any outstanding loan balance.
- $50,000 minus your highest outstanding TSP loan balance in the preceding 12 months.
The $10,000 floor in rule 2 protects employees with small balances: if your vested balance is $15,000, 50% = $7,500, which falls below $10,000 — so the effective cap becomes $10,000 (minus outstanding).
Two-loan rule (effective 2022): You may have up to two outstanding loans simultaneously — either two general-purpose loans, or one general-purpose plus one residential. Two residential loans are not permitted. After fully repaying a loan, a 60-day waiting period applies before a new loan can be taken.