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Formula
Each year: D = min(S × p, L + C(age)); A = 1% × S + min(D, 3% × S) + 0.5 × min(max(D − 3% × S, 0), 2% × S); each month: B = B × (1 + R)^(1/12) + (D + A) ÷ 12
- D
- your employee contribution for the year, capped at the IRS limit
- S
- your basic pay that year (raised each year by the annual raise)
- p
- your contribution rate as a share of basic pay
- L
- the elective deferral limit ($24,500 for 2026)
- C(age)
- the catch-up allowed at that age ($0 under 50, $8,000 from 50, $11,250 at 60–63 for 2026)
- A
- agency or service contributions (1% automatic plus matching); zero for CSRS and legacy uniformed services
- R
- the expected annual return; B is the account balance
What the Thrift Savings Plan is
The Thrift Savings Plan (TSP) is the defined-contribution retirement plan for federal civilian employees and members of the uniformed services, including the Ready Reserve. Congress created it in 1986 alongside the Federal Employees Retirement System (FERS), and it works much like a private-sector 401(k): you choose a percentage of basic pay to contribute, your agency or service may add money, and the account is invested in low-cost index funds until you retire.
For FERS employees the TSP is one of three retirement pillars, alongside the FERS basic annuity and Social Security. Under the Blended Retirement System (BRS) for the military, it sits next to a reduced pension. In both cases what you build in the TSP can make a large difference to retirement income.
How to use the TSP calculator
The TSP calculator needs only a few figures from your leave and earnings statement.
- Pick your retirement system. FERS and BRS receive agency contributions; choose the CSRS or legacy uniformed services option if you receive none.
- Enter your current age, the age you expect to retire or leave service, and your annual basic pay. Add an expected yearly raise, such as a typical step increase plus general pay adjustment.
- Enter the percentage of basic pay you contribute. If you choose a rate above what the IRS allows, the calculator caps each year at the limit for your age.
- Add your current TSP balance and an expected average annual return.
- The limit fields are prefilled with 2026 IRS figures. Change them to model another year.
The results show the estimated balance at retirement, the split between your money, agency money and growth, and a year-by-year table. If you contribute less than 5%, a note reminds you that part of the match is going unclaimed.
How agency matching contributions work
The tsp.gov schedule for FERS and eligible BRS participants is:
| You contribute | Automatic 1% | Agency match | Total agency money | Total going in |
|---|---|---|---|---|
| 0% | 1% | 0% | 1% | 1% |
| 1% | 1% | 1% | 2% | 3% |
| 2% | 1% | 2% | 3% | 5% |
| 3% | 1% | 3% | 4% | 7% |
| 4% | 1% | 3.5% | 4.5% | 8.5% |
| 5% | 1% | 4% | 5% | 10% |
| Over 5% | 1% | 4% | 5% | Your % + 5% |
Matching is based on what you contribute each pay period. If you reach the annual limit before the last paycheck of the year, the match stops for the remaining pay periods, so spreading contributions across the full year keeps the full match. BRS members start receiving the 1% after 60 days of service and matching after two years. CSRS employees and members under the legacy military retirement system do not receive agency contributions.
Catch-up and the 2026 limits
The TSP shares the IRS elective deferral limit with 401(k) and 403(b) plans: $24,500 for 2026. From the year you turn 50 you can contribute an extra $8,000, and in the years you turn 60 through 63 the catch-up rises to $11,250. Catch-up contributions are eligible for matching, within the 5% of pay limit. From 2026, if your prior-year wages from TSP-eligible federal service were above $150,000, your catch-up contributions must go into the Roth balance.
TSP funds and the return to enter
The TSP offers five individual funds and a series of Lifecycle (L) Funds:
- G Fund: specially issued Treasury securities paying a guaranteed rate of interest, reset monthly; the lowest expected return.
- F Fund: a portfolio of government and corporate bonds.
- C Fund: 500 of the largest U.S. companies.
- S Fund: over 3,000 small and mid-sized U.S. companies.
- I Fund: over 5,000 companies in 44 foreign countries.
- L Funds: target-date mixes of the five funds that shift toward the G and F Funds as the target year approaches.
The return you enter should reflect your mix. An account held mostly in the G Fund will grow far more slowly than one in the C, S and I Funds, and stock-heavy mixes swing more from year to year. Try a cautious rate and your expected rate to see a range.
TSP growth calculation by hand
Take a FERS employee earning $62,000 who contributes 5% ($3,100). The agency adds 1% ($620) plus a 4% match ($2,480), so $6,200 goes in each year. At a 6% return for 25 years with no starting balance:
- Growth factor: ((1.06)^25 − 1) ÷ 0.06 = 54.8645
- Balance: $6,200 × 54.8645 ≈ $340,160
Half of that, about $170,080, traces back to agency money. The TSP calculator also raises pay each year and adds money monthly, so its answer will differ slightly from this shortcut.
Projected TSP balance by starting age
From the TSP growth calculator above: FERS, $75,000 basic pay rising 2% a year, no starting balance, a 6% return, retiring at 62.
| Starting age | 0% (1% only) | 3% | 5% | 10% |
|---|---|---|---|---|
| 25 | $126,258 | $883,809 | $1,262,584 | $1,893,875 |
| 35 | $60,004 | $420,031 | $600,044 | $900,066 |
| 45 | $24,894 | $174,261 | $248,944 | $373,416 |
Going from 0% to 5% multiplies the balance by ten, because your 5% unlocks another 4% from the agency on top of the automatic 1%.
Common mistakes
- Contributing under 5%. Anything less leaves free agency money unclaimed.
- Front-loading the year. Hitting the limit early can stop matching for the rest of the year.
- Leaving everything in the G Fund for decades. It is stable but may not keep pace with inflation over a long career.
- Forgetting the Roth catch-up rule if your prior-year federal wages were above the threshold.
Compare with a nonprofit or public-school plan using the 403(b) calculator, check overall readiness with the retirement calculator, or see how compounding works on its own with the compound interest calculator.
Worked examples
A FERS employee taking the full match
FERS, age 28, $68,000 basic pay rising 2% a year, 5% contributed (so the agency adds 1% + 4%), $9,000 already in the TSP, 6.5% average return, retiring at 62.
Inputs: Retirement system = FERS civilian (1% automatic + up to 4% match); Current age = 28 years; Retirement age = 62 years; Annual basic pay = $68000; Expected annual raise = 2 %; Your contribution = 5 % of pay; Current TSP balance = $9000; Expected annual return = 6.5 %; Catch-up contributions from age 50 = Yes, allow catch-up when my % exceeds the limit; Elective deferral limit (402(g)) = $24500; Age 50+ catch-up limit = $8000; Age 60–63 catch-up limit = $11250; Annual additions limit (415(c)) = $72000
Year 1 employee contribution: min($68,000.00 × 5%, limit at age 28 $24,500.00) = $3,400.00 Agency automatic 1%: $68,000.00 × 1% = $680.00 Agency match: 100% of the first 3% of pay + 50% of the next 2% = $2,720.00 Monthly growth rate: (1 + 6.5%)^(1/12) − 1 = 0.5262% Each month: balance × (1 + monthly rate) + (your + agency contributions) ÷ 12, repeated for 408 months
Answer: Contributing 5% of $68,000.00 basic pay from age 28 to 62 at a 6.5% return, the TSP grows to an estimated $1,095,276.17 (you $163,314.93, agency $163,314.93, growth $759,646.32).
A service member under BRS saving 10%
BRS, age 22, $41,000 basic pay rising 3% a year, 10% contributed, no starting balance, 7% return, leaving service at 42.
Inputs: Retirement system = Blended Retirement System (1% automatic + up to 4% match); Current age = 22 years; Retirement age = 42 years; Annual basic pay = $41000; Expected annual raise = 3 %; Your contribution = 10 % of pay; Current TSP balance = $0; Expected annual return = 7 %; Catch-up contributions from age 50 = Yes, allow catch-up when my % exceeds the limit; Elective deferral limit (402(g)) = $24500; Age 50+ catch-up limit = $8000; Age 60–63 catch-up limit = $11250; Annual additions limit (415(c)) = $72000
Year 1 employee contribution: min($41,000.00 × 10%, limit at age 22 $24,500.00) = $4,100.00 Agency automatic 1%: $41,000.00 × 1% = $410.00 Agency match: 100% of the first 3% of pay + 50% of the next 2% = $1,640.00 Monthly growth rate: (1 + 7%)^(1/12) − 1 = 0.5654% Each month: balance × (1 + monthly rate) + (your + agency contributions) ÷ 12, repeated for 240 months
Answer: Contributing 10% of $41,000.00 basic pay from age 22 to 42 at a 7% return, the TSP grows to an estimated $327,329.26 (you $110,168.54, agency $55,084.27, growth $162,076.46).
Edge case: no agency contributions, maxing out with catch-up
CSRS-style account with no agency money, age 59, $150,000 pay, asking for 25% ($37,500): capped at $32,500 at 59, $35,750 at 60–63 and $32,500 at 64–65. $520,000 balance, 4% return, retiring at 66.
Inputs: Retirement system = CSRS or legacy uniformed services (no agency contributions); Current age = 59 years; Retirement age = 66 years; Annual basic pay = $150000; Expected annual raise = 0 %; Your contribution = 25 % of pay; Current TSP balance = $520000; Expected annual return = 4 %; Catch-up contributions from age 50 = Yes, allow catch-up when my % exceeds the limit; Elective deferral limit (402(g)) = $24500; Age 50+ catch-up limit = $8000; Age 60–63 catch-up limit = $11250; Annual additions limit (415(c)) = $72000
Year 1 employee contribution: min($150,000.00 × 25%, limit at age 59 $32,500.00) = $32,500.00 Monthly growth rate: (1 + 4%)^(1/12) − 1 = 0.3274% Each month: balance × (1 + monthly rate) + (your + agency contributions) ÷ 12, repeated for 84 months
Answer: Contributing 25% of $150,000.00 basic pay from age 59 to 66 at a 4% return, the TSP grows to an estimated $960,850.73 (you $240,500.00, agency $0.00, growth $200,350.73).
Assumptions and limitations
- Results are estimates for planning, not financial, tax or investment advice. TSP fund returns vary from year to year; only the G Fund pays a guaranteed rate of interest.
- FERS and BRS receive the 1% automatic contribution and matching on the first 5% of pay (dollar for dollar on 3%, 50 cents per dollar on the next 2%) from the first year. BRS waiting periods (60 days for the 1% and two years for matching) and vesting are not modeled.
- Contributions are paid in 12 equal end-of-month amounts, and the balance grows monthly at the rate equivalent to your annual return compounded once a year.
- Your age goes up by one each year, starting at the current age you enter. Catch-up starts in the year you are 50, the higher catch-up applies at 60 to 63, and the regular catch-up applies again from 64. Catch-up dollars count toward the 5% that is matched.
- IRS limits are held at the values you enter (2026 figures by default) for every year, so long projections may understate what you are allowed to contribute after future inflation increases.
- Traditional and Roth contributions are treated the same; taxes, loans, withdrawals, inflation and pay above the limits on incentive or bonus pay are not modeled.
Frequently asked questions
How is the TSP agency match calculated?
If you are under FERS or are an eligible BRS member, your agency or service puts in 1% of basic pay automatically, then matches your first 3% dollar for dollar and the next 2% at 50 cents per dollar. Contribute 5% and the agency adds 5% in total; contribute 3% and it adds 4%.
What is the TSP contribution limit for 2026?
The elective deferral limit for 2026 is $24,500, the same as for 401(k) and 403(b) plans. From the year you turn 50 you can add up to $8,000 in catch-up contributions, or $11,250 in the years you turn 60, 61, 62 or 63. Agency contributions do not count toward the $24,500.
Do military members get a TSP match?
Members under the Blended Retirement System receive the 1% automatic contribution after 60 days of service and matching contributions after two years of service, on the same 3% plus 2% schedule as FERS. Members under the legacy retirement system do not receive agency contributions; choose that option to model them.
Should I choose Roth TSP or traditional TSP?
Traditional contributions lower your taxable pay now and are taxed when withdrawn, while Roth contributions are taxed now and qualified withdrawals are tax-free. The agency match always goes into the traditional balance. This calculator projects the account balance and does not estimate taxes, so the choice does not change the result shown.
What return should I use for the TSP?
Use a long-run average that fits your fund mix, after the small TSP expense ratio. A portfolio mostly in the G Fund will grow far more slowly than one mostly in the C, S and I Funds. Running the calculator at a few different rates gives a range rather than one number.
How long will my TSP last after I retire?
This page projects the balance on the day you retire. To see how long that balance might last with regular withdrawals, use the retirement withdrawal calculator, and see tsp.gov for the TSP's own annuity calculator.
How do I calculate TSP growth by hand?
Add your yearly contribution and the agency's, then multiply by ((1 + r)^n − 1) ÷ r, where r is the yearly return and n the number of years, and add any current balance × (1 + r)^n. This assumes deposits once a year, so it is a little lower than the calculator's monthly result.
Sources
- What is a contribution? — Thrift Savings Plan (Federal Retirement Thrift Investment Board). Checked October 10, 2026.
- Making contributions — Thrift Savings Plan (Federal Retirement Thrift Investment Board). Checked October 10, 2026.
- Traditional and Roth TSP contributions — Thrift Savings Plan (Federal Retirement Thrift Investment Board). Checked October 10, 2026.
- What is an individual fund? — Thrift Savings Plan (Federal Retirement Thrift Investment Board). Checked October 10, 2026.
- 401(k) limit increases to $24,500 for 2026, IRA limit increases to $7,500 (IR-2025-111) — Internal Revenue Service. Checked October 10, 2026.
- Retirement topics — Catch-up contributions — Internal Revenue Service. Checked October 10, 2026.