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What this site does

It replays a plan of where your money sits, month by month, against the TSP's own daily share prices since June 2, 2003, and shows what the plan would have done. It is history, not advice: it cannot see ahead, and nothing here tells you what to buy.

The funds, one line each

G Fund

Special interest-bearing Treasury securities issued only to the TSP. Their rate is the average market yield of marketable Treasury debt not due or callable within four years, set each month from the end of the month before.

F Fund

An index fund designed to track the Bloomberg U.S. Aggregate Bond Index.

C Fund

An index fund designed to track the S&P 500 Index, holding each stock in proportion to its market value.

S Fund

An index fund designed to track the Dow Jones U.S. Completion Total Stock Market Index: U.S. stocks outside the C Fund's index, each in proportion to its market value.

I Fund

An index fund of stock markets outside the United States, each stock in proportion to its market value. Through July 31, 2024 it tracked the MSCI EAFE Index; since then it tracks the MSCI ACWI IMI ex USA ex China ex Hong Kong Index, so returns before and after that date follow different indexes.

L Income

The most conservative L Fund mix, for money being drawn down now. Every other L Fund merges into it when it retires.

L 2030 to L 2075

A mix of the G, F, C, S and I Funds that becomes steadily more conservative as its target year nears. When its mix matches the L Income Fund it retires and merges into L Income, on June 30 of its target year.

Two ways to change where your money is

Your investment election sets where new money goes: contributions, loan payments and rollovers. There is no limit on how often you change it, and a change normally takes effect the next business day.

An interfund transfer moves money already in your account. It leaves your investment election alone, so new money keeps going where it went before.

• You get two transfers a calendar month. After that: G Fund only, until the next calendar month.
• A transfer counts in the month of its posting date, not the month you asked for it.
• The rules name two kinds of transfer, and both count toward the two. A fund reallocation sets new percentages for the whole balance. A fund transfer moves part of the balance, in percent or dollars, from some funds into others.

The plans on this site are interfund transfers of the whole balance. They add no new money.

Which day your move happens

The cutoff is 12:00 noon Eastern Time on a business day.

• A transfer asked for before the cutoff normally posts the same business day.
• One asked for at or after the cutoff normally posts on the next business day.
• One asked for on a day that is not a business day, such as a Saturday, normally posts on the next business day.

In each case, the money moves at the share price of the posting date. Two examples from the price file:

• Asked for after the cutoff on Friday, October 9, 2026, a transfer would post on Tuesday, October 13, because Monday, October 12 was Columbus Day.
• Asked for after the cutoff on Wednesday, December 31, 2025, a transfer would post on Friday, January 2, 2026, because Thursday, January 1 was New Year's Day, and it would count as one of January's two.

The rules say "ordinarily": things outside the TSP's control, such as power outages, the failure of telephone service, unusually heavy transaction volume and acts of God, can hold a request up, so the TSP cannot promise a day.

Days with no share price

A weekday has no share price on the New York Stock Exchange's holidays. Nor does it on two federal holidays on which stocks still trade:

• Columbus Day, the second Monday in October: Monday, October 12, 2026 and Monday, October 11, 2027.
• Veterans Day, November 11: Wednesday, November 11, 2026 and Thursday, November 11, 2027.

When November 11 falls on a Saturday, the Friday before still has a price. When it falls on a Sunday, the Monday after has none. A handful of other weekdays in the price file have no price either.

This site counts priced days only. So the 8th trading day of October 2026 was October 13, though on a stock-market calendar it was October 12.

The rules define a business day as any calendar day for which share prices are calculated. So the official price file is the last word: a day with no price in it is not a business day on this site.

Why the months don't add up to the year

The twelve months add up to 23.0%, but the year gave 25.0%: $10,000 became $12,496. Each month's percent is of a balance that already holds the months before, so each gain is earned on the gains before it.

It can go the other way. In 2020 the C Fund's months add up to 20.0%, but the year gave 18.3%. By the end of March, $10,000 had fallen to $8,035, so April's 12.8% rise was earned on $8,035, not on $10,000.

A simple case: up 50%, then down 50%, leaves $10,000 at $7,500.

Growth per year is not the average year

The C Fund fell 37.0% in 2008 and rose 26.7% in 2009. That averages −5.2% a year, yet $10,000 became $7,982: −10.7% a year.

• The headline on every result is growth per year: the one steady yearly rate that takes the start balance to the end balance. The average year is under "All the numbers" on the backtester, in Advanced.
• A year marked with an asterisk is only part of a year, such as the current one, which runs to the latest price. It is kept out of the yearly averages.

Fitted and unseen years

Every result is split at 2018. The years before it are the fitted years: the years a plan could have been tuned to, and the years the strategies page picks its shortlist of plans on. The years from 2018 on are the unseen years: no plan on the shortlist was picked on them, so read that figure first. You can move the split in Advanced.

How to read a backtest says why.

Where to go next

• The backtester, with the example plan: change a month and see what it does.
• How TSP interfund transfers work: the rules in full.
• How to read a backtest: what a result can and cannot tell you.
• The glossary: every term on the site, in a sentence or two.