TSP Calculator Help
What each field means, where to find your numbers, and how to read the results.
What this calculator does
The TSP calculator projects how much your Thrift Savings Plan account could be worth at retirement based on what you have now, what you and your agency will add over time, and how much that money might grow.
It uses a year-by-year compound growth model. Each year, your existing balance grows at the expected annual return you enter. Your employee contributions and agency contributions are added at mid-year (a standard approximation), and those also earn partial-year returns. After the number of years you specify, the calculator shows your projected ending balance.
From that balance, two income estimates follow. The 4% rule calculation multiplies the final balance by 4% and divides by 12 to show a monthly income figure. This comes from the Trinity Study, which analyzed historical stock and bond returns to find a withdrawal rate with a high probability of lasting 30 years. It is a planning benchmark, not a promise.
The calculator also breaks down where the projected balance comes from: how much is your own contributions, how much is agency contributions, and how much is investment growth. That breakdown matters because it shows you the compounding effect of starting early and capturing the full agency match.
If you enter a Roth percentage greater than zero, the calculator splits the final balance proportionally to show an estimated Traditional and Roth balance. Keep in mind that agency contributions always go to Traditional regardless of your election, so the Roth split in the output is an approximation of the distribution of your total balance, not a precise legal accounting.
What the calculator does not model: future salary increases, changes to contribution amounts over time, inflation adjustments, or tax effects on withdrawals. It holds your inputs constant for the full projection period. The results are estimates for planning purposes.
Input guide
Current TSP balance
Log into tsp.gov and find your account balance on the main dashboard. If you have both a Traditional and Roth TSP balance, use the total combined figure. New federal employees with no balance yet should enter $0. The calculator works from any starting point.
Annual salary
Use your annual basic pay rate, which you can find on your most recent SF-50 (Notice of Personnel Action) in block 20, or on your pay stub. This number is used to calculate the dollar amount of your agency match. Do not include overtime, bonuses, or allowances. Most federal pay schedules list basic pay separately from total compensation.
Annual employee contribution
This is what you contribute to TSP from your paychecks over a full year. Multiply your per-paycheck contribution by the number of pay periods you have in a year (26 for biweekly, 24 for semimonthly). Your current election percentage and dollar amount are on tsp.gov under Contribution Details, or in your HR system (MyPay for most civilian employees).
The 2026 IRS limit for employee elective deferrals is $23,500. If you're 50 or older, you can contribute an additional $7,500 in catch-up contributions for a total of $31,000 from your own paycheck. The calculator will flag if you enter an amount above $23,500 as a reminder to verify your eligibility for the catch-up limit.
Agency match (% of salary)
For most FERS employees, the maximum agency contribution is 5% of your basic pay: 1% automatic (deposited regardless of what you contribute) plus up to 4% in matching contributions (dollar-for-dollar on your first 3%, then 50 cents on your next 2%). The slider goes up to 5% because that is the FERS maximum. CSRS employees do not receive agency matching contributions, so enter 0 if you are CSRS.
The calculator shows the dollar amount of agency contributions at your current salary. If you contribute less than 5% of your salary, a note appears showing how much additional agency match you're leaving uncaptured.
Years until retirement
The number of full years between now and when you plan to retire and stop contributing to TSP. If you plan to retire in 2046 and it's 2026, enter 20. For shorter timeframes, even 5 or 10 years can show meaningful growth, especially if you have a substantial existing balance.
Expected annual return
The average annual rate of return you expect your TSP investments to earn over the projection period. This is the most consequential assumption in the calculator. A few reference points: the C Fund (S&P 500 index) has averaged roughly 10% annually since 1988; the G Fund has averaged 3-4% annually with no principal risk; a typical blended allocation (60% C, 20% S, 20% G) has historically been around 7-8%. Lower this number for more conservative projections.
Roth percentage of contributions
The percentage of your employee contributions going into Roth TSP rather than Traditional TSP. If you contribute 100% to Traditional, set this to 0. If you split 50/50, set it to 50. This only affects how your projected balance is displayed as a Traditional/Roth split. Agency contributions always go to Traditional, so even 100% Roth contribution elections will result in some Traditional balance from the agency match.
Output guide
Projected TSP balance at retirement
The estimated total value of your account on the day you retire, combining your current balance, all future contributions, and investment growth at the rate you entered. This is a nominal figure: it has not been adjusted for inflation. A balance of $1 million in 2046 will have less purchasing power than $1 million today.
Projected monthly income (4% rule)
The projected balance multiplied by 4%, then divided by 12. This is the monthly withdrawal amount the 4% rule suggests is sustainable over a 30-year retirement based on historical market returns. If your retirement could last 35 or 40 years, some planners recommend using 3-3.5% instead. If you have a FERS pension and Social Security, you may need less from TSP than this figure implies.
Where the money comes from
A breakdown of your projected balance into three pieces: your own contributions over the projection period, agency contributions over the same period, and investment growth. This breakdown shows why starting early matters. In most long-horizon projections, investment growth is the largest component by a wide margin.
Traditional and Roth balance split
Shown when your Roth percentage is above zero. The calculator allocates your total projected balance proportionally based on your Roth election. Agency contributions are treated as Traditional regardless of your election. The split is an approximation. Your actual Traditional and Roth balances will depend on the specific amounts contributed to each in each year, plus the respective investment returns on each sub-account.
Frequently asked questions
What does the 4% rule mean in the TSP calculator?
The 4% rule is a guideline from financial research suggesting you can withdraw 4% of your portfolio in the first year of retirement, then adjust for inflation each year, with a high probability of not running out of money over a 30-year retirement. The calculator multiplies your projected balance by 0.04, then divides by 12 to show a monthly income estimate. It's a starting point, not a guarantee.
Why do agency contributions always go to Traditional TSP?
Federal law requires that agency contributions, both the 1% automatic and the matching contributions, go into the Traditional side of your TSP account. You cannot redirect agency contributions to Roth TSP. Even employees who contribute 100% to Roth will have some Traditional balance from agency contributions.
Where do I find my current TSP balance?
Log in at tsp.gov. Your balance appears on the main dashboard. If you have both Traditional and Roth balances, the site shows them separately. Use the total combined balance as your starting figure in the calculator.
How does the calculator handle inflation?
The calculator uses nominal returns, not inflation-adjusted returns. A 7% return input means 7% nominal growth per year. To estimate real purchasing power, subtract roughly 2.5-3% from your expected return. At 7% nominal and 3% inflation, your real return is approximately 4%, and the projected balance should be mentally discounted accordingly.
Does the calculator account for future salary increases?
No. The calculator holds your salary and contribution amounts constant throughout the projection period. Federal pay typically increases over time via step increases and locality adjustments, which would raise both contributions and agency match. The results are a conservative baseline. To account for expected pay growth, you can run the calculator twice: once with your current numbers, once with projected future salary figures.