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TSP Tools

TSP glossary

The words used on this site, in the order you are likely to meet them.

Backtesting

Backtest
A replay of a fixed plan against the share prices that were actually published, to see how it would have done. It answers "what happened", not "what will happen".
Strategy, or plan
A list of moves: a month, a day in that month, and the fund or mix of funds to hold from that day. A Simple plan is one fund per month, moved on the first business day.
Move
One transfer of the whole balance into a fund or a mix of funds on a given day. A move into the G Fund alone does not count against the monthly limit.
Mix
A split across funds bought on one day, for example half C Fund and half S Fund. After the purchase each half grows at its own fund's rate until the next move.
Drift
What a mix does between moves: the faster-growing fund becomes a larger share of the balance, because nothing rebalances it.
Benchmark
The comparison line, usually the C Fund held all year. A plan that cannot beat a fund you could hold without lifting a finger is not earning its moves.
Growth per year
The compound annual growth rate: the single yearly rate that would take the starting balance to the ending balance over the exact time elapsed. The headline number on every result.
Total return
The ending balance over the starting balance, minus one, over the whole period tested.
Mean yearly return
The plain average of the full calendar years in the period. A partial year at the end is shown separately and left out of the average.
Median yearly return
The middle year when the full years are sorted. Less swayed than the mean by one great or terrible year.
Standard deviation (sample)
How far the yearly returns typically sit from their mean, computed with the sample formula (dividing by one less than the number of years). A higher number means a bumpier ride.
Best year and worst year
The full calendar years with the highest and lowest return. The worst year tells you more about what the plan asks of your nerves.
Biggest drop
The maximum drawdown: the largest fall from a daily peak to the following low before a new peak was reached. Measured on the daily balance, so it catches falls inside a year.
Beat the benchmark
The share of full years in which the plan returned more than its benchmark.
Moves a year
How many transfers the plan makes in a typical year. Each one is a chance to be wrong about the day.
Out-of-sample
Years the plan was not judged on. By default the result is split at 2018: the earlier years are the training period, the later years are the test. A plan that only works in the years it was picked from has learned the past, not the market.
Since saved
For a saved strategy, its return from the day it was saved against the benchmark over the same days. It is the one honest test, because nobody could peek at those prices in advance, and it grows every day.
Hindsight bias
The tendency to believe a plan that fits the past would have been obvious at the time. Every leaderboard invites it.
Overfitting
Choosing a plan because it matches the quirks of a particular stretch of history. The more plans are tried, the more the best one is luck.

The TSP

Share price
The daily price of one share of a fund, set after the market closes and published with four decimals. Every return on this site is computed from these prices.
Business day
A day on which share prices are set: any calendar day for which share prices are calculated. Weekends, stock-market holidays, Columbus Day and Veterans Day are not business days.
Interfund transfer
A move of money already in your account between funds, either a fund reallocation (the whole account) or a fund transfer (part of it). 2 unrestricted transfers a month, then G Fund only, until the next calendar month. See how interfund transfers work.
Noon cutoff
The 12:00 noon Eastern Time on a business day deadline: a request before it posts the same business day; at or after it, the next business day.
Contribution allocation
Where new money from your pay goes. Changing it does not move the balance you already hold and is not an interfund transfer.
Core funds
The G, F, C, S and I Funds. Each tracks one market, or in the G Fund's case holds special Treasury securities issued only to the TSP.
L Funds
Lifecycle funds: a mix of the core funds that becomes more conservative as the fund's target year nears. Each retires into the L Income Fund when its mix matches it.
I Fund benchmark change
The I Fund tracked one international index through mid-2024 and a broader one after. Backtests that use I before that date reflect the old index.

Contributions

Elective deferral limit
The most you may put in from your own pay in a calendar year across traditional and Roth together, set by the IRS each autumn. The current figure is on the contribution planner, with its source.
Catch-up contributions
Extra room above the elective deferral limit for anyone who turns 50 or older by the end of the year, with a higher amount for those aged 60 to 63 at year end.
Spillover
Since 2021 there is no separate catch-up election: contributions above the elective deferral limit simply continue, up to the catch-up limit, from basic pay only.
Roth catch-up requirement
A rule that makes catch-up contributions Roth-only for people whose prior-year wages from the same employer were above a threshold. The planner shows it when it applies to you.
Agency automatic contribution
The 1% of basic pay a FERS or Blended Retirement System employer puts in whether or not you contribute.
Agency match
Dollar for dollar on the first 3% of basic pay you contribute, then 50 cents on the dollar up to 5%: at most 4% of pay. Contributing less than 5% in any pay period leaves some of it on the table, and it is not made up later.
Annual additions limit
A second, higher IRS ceiling on everything that goes into your account in a year, your money and the agency's together.
Pay date
The day you are paid. Pay date decides the tax year: a pay period that ends in December but is paid in January counts in the new year.
Pay entry base date
For service members, the date that starts the clock on Blended Retirement System automatic and matching contributions.

Sources and dates checked

See also: how each statistic is computed.