TSP Calculator
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About the TSP Calculator
The Thrift Savings Plan is the retirement account for federal employees and uniformed service members — functionally a 401(k) with famously low costs. Its single most valuable feature is the FERS agency match: contribute 5% of salary and your agency contributes another 5%. That's an instant, guaranteed 100% return on those dollars before any market growth, and it's the first number this calculator gets right.
The projection math is standard compound growth, but the inputs deserve honesty: the often-cited ~10% figure is the C Fund's long-run historical average, not a promise, and most planners model at 6–8% to stay conservative. Run the calculator at two return rates and treat the gap as your uncertainty band.
Want to isolate pure compounding without the match rules? Use our Compound Interest Calculator
The FERS Agency Match, Percentage by Percentage
What the agency adds at each contribution level — the jump from 0% to 5% is the highest-yield decision in federal employment:
| You contribute | Agency adds | Total going in |
|---|---|---|
| 0% | 1% (automatic) | 1% |
| 1% | 2% (1% auto + 1% match) | 3% |
| 3% | 4% (1% auto + 3% match) | 7% |
| 5% | 5% (1% auto + 3% + 2×0.5%) | 10% |
| 10% | 5% (match caps at 5%) | 15% |
Read the last two rows carefully: the match maxes out at 5% — so the leap from contributing 3% to 5% doubles your total inflow from 7% to 10% of salary, while every percent beyond 5% adds only itself. Contributing less than 5% is declining free money; the calculator shows exactly how much.
How the Projection Works
Three moving parts, compounded monthly:
- Your current balance grows at the expected return for the full period.
- Monthly contributions (your % + agency % of salary ÷ 12) are added and each compounds from its own start date.
- The agency portion is computed from the official FERS formula automatically — you only enter your own percentage.
What the model deliberately leaves out: salary raises, the IRS elective deferral limit, and Roth-vs-traditional tax treatment. All three matter at the margins — but return rate and years invested dominate the outcome by an order of magnitude.
Where TSP Money Actually Grows: The Funds
TSP offers five core index funds — G (government securities, never loses nominal value), F (bonds), C (S&P 500), S (small/mid caps), I (international) — plus Lifecycle (L) funds that glide between them by target date. Your expected-return input should reflect your mix: an all-G portfolio has historically returned far less than a C-heavy one, with far less volatility.
The quiet TSP superpower is cost: expense ratios run a few hundredths of a percent, among the lowest anywhere. On a $500,000 balance, the difference between TSP-level fees and a typical 1%-fee managed account is roughly $5,000 per year — compounding in your favor for decades.
Frequently Asked Questions
How does the TSP agency match work?
Under FERS: your agency automatically contributes 1% of salary even if you contribute nothing, matches your first 3% dollar-for-dollar, and adds 50 cents per dollar on the next 2%. Contribute 5% and the agency adds 5% — a guaranteed instant doubling of those contributions. Beyond 5%, additional contributions earn no extra match.
Does TSP double every 7 years?
Only at roughly a 10.3% annual return (the Rule of 72: 72 ÷ return ≈ doubling years). The C Fund's long-run history is near that, so an aggressive allocation has doubled roughly every 7 years historically — but the G Fund at ~4% doubles in about 18 years. Your doubling speed is your allocation, not a TSP property.
How much should I have in my TSP at 40?
A widely used benchmark (Fidelity's) is 3× your salary saved by 40 across retirement accounts — $240,000 on an $80,000 salary. If you're behind, the leverage is contribution rate and time: raising contributions from 5% to 10% on that salary at 7% adds roughly $190,000 over 20 years. Benchmarks are direction, not verdicts.
What is the 4% rule for TSP?
A retirement-spending heuristic: withdraw 4% of the balance in year one, adjust for inflation annually, and the portfolio has historically lasted 30+ years. Inverted, it sizes your target: yearly spending ÷ 0.04 — $70,000/year needs about $1.75 million. It's a planning rule of thumb from historical U.S. data, not a guarantee.
What return rate should I use in the projection?
Model twice: 6–7% as a conservative planning case, and 9–10% as an aggressive historical case (C Fund territory). The honest answer is a range, not a number — and if a 2-point return difference changes your retirement date by years, your contribution rate is doing too little of the work.
Is the TSP a 401(k)?
Functionally yes — same tax treatment (traditional and Roth options), same annual IRS elective deferral limits, employer match, early-withdrawal rules. The differences favor TSP: index-fund expense ratios measured in hundredths of a percent, the unique G Fund (government securities that can't lose nominal value), and simple Lifecycle funds.
Should I contribute more than 5% to TSP?
The first 5% is unambiguous — it's matched 1:1 in total and refusing it is declining salary. Beyond 5%, TSP remains excellent (ultra-low fees, tax advantages), and the usual hierarchy is: 5% TSP → high-interest debt → then more TSP up to the IRS limit. Run this calculator at 5% vs 10% to price the difference in retirement dollars.
Does this calculator include military BRS matching?
Yes in structure — the Blended Retirement System uses the same formula (1% automatic + up to 4% matching = 5% total at a 5% contribution). BRS differences are timing-based: automatic contributions start after 60 days of service and matching after 2 years. Model your current contribution rate and it applies directly.
Sources & References
- [1]Maximize your savings (agency match rules) — Thrift Savings Plan (official, FRTIB)
- [2]Compound interest calculator — U.S. Securities and Exchange Commission - Investor.gov
Methodology. This calculator uses standard financial formulas used across the industry. It is reviewed and maintained by the Vast Calculators editorial team.
Last updated · July 2026
Disclaimer. This tool provides estimates for general informational purposes only and is not a substitute for professional financial advice. Always consult a qualified financial advisor before making decisions about your finances.