THRIFT SAVINGS PLAN
Five TSP funds, thousands of MFW options, and no built-in framework for choosing.
The TSP is exceptional. The Mutual Fund Window adds breadth most participants can’t systematically evaluate. This page covers how both work, what they cost, and what disciplined allocation looks like.
No account access. No minimums. We'll only email you about early access.
- The five core TSP funds
- G, F, C, S, and I — the foundation of the TSP for most participants, with expense ratios among the lowest available anywhere.
- The Mutual Fund Window
- Eligible participants gain access to thousands of mutual funds beyond the core five — actively managed, sector-specific, and asset classes the core lineup doesn’t cover.
- The hidden costs of the MFW
- Transaction fees, expense-ratio variability, and minimum holding periods make the MFW a deliberate-allocation discipline — not a fee-free trading account.
- Allocation discipline
- A systematic approach to MFW investing accounts for transaction costs, expense ratios, and holding-period constraints — not just expected return in isolation.
THE COMPLETE GUIDE
Everything to know about the TSP Mutual Fund Window.
How the MFW works, who qualifies, what it costs, and why allocation decisions inside the Mutual Fund Window require a different discipline than the core TSP funds. Background reading from Weisert Investments, the Registered Investment Advisor behind investment.tips.
Read the full guideFrequently asked questions
What is the TSP Mutual Fund Window?
The Mutual Fund Window (MFW) is an opt-in feature of the Thrift Savings Plan that lets eligible participants invest a portion of their TSP balance in thousands of mutual funds beyond the five core TSP funds (G, F, C, S, and I). The MFW operates alongside the standard TSP menu, not as a replacement for it. Participants who opt in can hold both core TSP allocations and MFW allocations at the same time.
Who qualifies for the TSP Mutual Fund Window?
MFW access is available to TSP participants who meet specific eligibility rules: a minimum standard TSP account balance, an allocation ceiling on how much of the account can be invested through the MFW, and active TSP participation status. The TSP website and your agency’s benefits office are the authoritative sources for current thresholds, which are subject to change. Log in to your TSP account dashboard to see whether the MFW option is available to you.
How is the Mutual Fund Window different from the five core TSP funds?
The core TSP funds are passive index funds (plus the unique G Fund) with expense ratios among the lowest available anywhere. The MFW adds access to thousands of mutual funds spanning actively managed strategies, sector funds, commodity funds, REITs, and other categories the core lineup doesn’t cover. MFW funds carry their own — typically higher — expense ratios, and the TSP charges a per-transaction fee each time you move money into or out of an MFW fund.
How often should TSP MFW allocations change?
Less frequently than a fee-free brokerage mindset suggests. The MFW’s transaction fee structure creates a real cost for every allocation change — that cost has to be earned back through better returns before the change adds value. A disciplined approach acts on genuine shifts in the expected-return environment, not on routine market fluctuations. In practice, a well-run MFW strategy typically involves a handful of significant allocation changes per year.