TSP Fund Comparison Guide: Understanding Every TSP Fund for Smarter Investing

Understanding the TSP Fund Lineup

The Thrift Savings Plan (TSP) is the retirement savings plan for federal employees and members of the uniformed services. With over $800 billion in assets and nearly 7 million participants, it is one of the largest defined contribution plans in the world. Its greatest advantage? Rock-bottom expense ratios that no commercial 401(k) can match.

But the TSP's simplicity — just five individual funds and a series of lifecycle funds — can be deceiving. Understanding how each fund works, how they relate to each other, and how to combine them effectively is essential for building a portfolio that matches your goals. This TSP fund comparison guide breaks down everything you need to know.

The Five Individual TSP Funds

The TSP offers five individual investment funds, each tracking a different segment of the financial markets. Together, they cover government bonds, investment-grade bonds, U.S. large-cap stocks, U.S. small and mid-cap stocks, and international stocks.

G Fund — government securities Investment Fund

The G Fund is unique in all of investing. It invests in a special non-marketable U.S. Treasury security issued exclusively to the TSP and is not available to the public. These securities guarantee the return of principal — you cannot lose money in the G Fund — while paying interest rates comparable to intermediate-term Treasury bonds.

This combination of zero principal risk with medium-term bond yields makes the G Fund unlike any other investment vehicle available anywhere. A comparable Treasury money market fund would offer lower yields, while an intermediate-term bond fund would carry interest rate risk. The G Fund gives you the yield without the risk.

• Benchmark: Specially issued U.S. Treasury securities
• Risk level: Lowest — no risk of principal loss
• Expense ratio: Approximately 0.05% (2026)
• Best for: Capital preservation, near-retirement participants, risk-averse investors
• Historical return range: 1.0% to 5.0% annually depending on interest rate environment

F Fund — Fixed Income Index Investment Fund

The F Fund tracks the Bloomberg U.S. Aggregate Bond Index, providing exposure to the broad investment-grade U.S. bond market. This includes Treasury bonds, government agency bonds, corporate bonds, and mortgage-backed securities. Unlike the G Fund, the F Fund carries interest rate risk — when rates rise, bond prices fall, and the F Fund's value can decline.

The F Fund's advantage over the G Fund is its potential for capital appreciation during periods of falling interest rates. When the Federal Reserve cuts rates or when investors flee to bonds during market turmoil, the F Fund can deliver returns significantly above what the G Fund offers. However, as 2022 demonstrated, it can also post meaningful losses when rates rise sharply.

• Benchmark: Bloomberg U.S. Aggregate Bond Index
• Risk level: Low to moderate — interest rate and credit risk
• Expense ratio: Approximately 0.05%
• Best for: Diversification, rate-decline environments, moderate risk tolerance
• Historical return range: -13% to +18% annually

C Fund — Common Stock Index Investment Fund

The C Fund tracks the S&P 500 index and is the large-cap equity pillar of the TSP. It holds the 500 largest publicly traded U.S. companies, weighted by market capitalization. The C Fund is what most TSP participants think of when they think of "stocks" — it captures the performance of corporate America's biggest and most established companies.

The C Fund has been the best-performing TSP fund over the past decade, driven by the dominance of large-cap technology stocks. However, this outperformance is not guaranteed to continue. Large-cap dominance runs in cycles, and there have been extended periods (2000-2010, for example) when the C Fund significantly underperformed small caps and international stocks.

• Benchmark: S&P 500 Index
• Risk level: Moderate to high — full equity market risk
• Expense ratio: Approximately 0.05%
• Best for: Long-term growth, core equity allocation
• Historical return range: -37% to +33% annually

S Fund — Small/Mid Cap Stock Index Investment Fund

The S Fund tracks the Dow Jones U.S. Completion Total Stock Market Index, which includes all U.S. stocks not in the S&P 500. This means the S Fund covers mid-cap and small-cap companies — roughly 3,400 stocks that complement the C Fund. Together, the C Fund and S Fund approximate the total U.S. stock market.

The C Fund vs S Fund comparison is one of the most debated topics among TSP investors. The S Fund tends to be more volatile than the C Fund but has historically delivered higher returns over very long periods. Small and mid-cap stocks are also more sensitive to economic cycles, tending to outperform during economic recoveries and underperform during recessions.

• Benchmark: Dow Jones U.S. Completion Total Stock Market Index
• Risk level: High — greater volatility than C Fund
• Expense ratio: Approximately 0.05%
• Best for: Aggressive growth, diversification beyond large caps
• Historical return range: -39% to +44% annually

I Fund — International Stock Index Investment Fund

The I Fund tracks the MSCI Europe, Australasia, Far East (EAFE) Index, providing exposure to large-cap stocks in developed international markets. Key countries include Japan, the United Kingdom, France, Germany, Switzerland, and Australia. Notably, the I Fund does not include emerging markets like China, India, or Brazil.

International diversification matters because U.S. and foreign stock markets do not move in lockstep. Currency fluctuations add another dimension — the I Fund's returns are affected by the value of the U.S. dollar relative to foreign currencies. When the dollar weakens, the I Fund gets a tailwind; when the dollar strengthens, it faces a headwind.

• Benchmark: MSCI EAFE Index
• Risk level: High — equity risk plus currency risk
• Expense ratio: Approximately 0.05%
• Best for: international diversification, weak-dollar environments
• Historical return range: -41% to +39% annually

TSP Fund Comparison: How the Funds Stack Up

Comparing the five TSP funds across key dimensions reveals their distinct characteristics and how they complement each other in a portfolio.

Return Potential

From highest to lowest expected long-term return: S Fund > C Fund > I Fund > F Fund > G Fund. This ordering reflects the equity risk premium — stocks are expected to return more than bonds over time because they carry more risk. Within equities, smaller companies (S Fund) carry a size premium over large caps (C Fund), though this premium has been inconsistent in recent decades.

Volatility and Risk

From highest to lowest volatility: S Fund > I Fund > C Fund > F Fund > G Fund. The S Fund has historically experienced the widest swings in annual returns. The I Fund's volatility is amplified by currency movements. The G Fund stands alone with zero volatility relative to principal preservation.

Correlation Between Funds

Understanding how TSP funds move relative to each other is critical for portfolio construction:

• C Fund and S Fund: Highly correlated (typically 0.85-0.90). They tend to move in the same direction, though the S Fund moves with greater magnitude. Holding both provides diversification benefits, but do not expect them to behave differently during market crises.
• C Fund and I Fund: Moderately to highly correlated (typically 0.75-0.85). International stocks provide meaningful diversification, especially during periods of dollar weakness or regional economic divergence.
• Equity funds and F Fund: Low to moderate correlation (typically 0.0-0.30). Bonds and stocks frequently move in opposite directions, making the F Fund a true diversifier. However, this negative correlation is not guaranteed — in 2022, both stocks and bonds fell simultaneously.
• G Fund and equity funds: Near-zero correlation. The G Fund moves independently of all other funds, making it the ultimate portfolio stabilizer.

Expense Ratios

All five TSP funds share essentially the same ultra-low expense ratio — approximately 0.05% as of 2026. This is a massive competitive advantage. A comparable portfolio of index funds in a commercial 401(k) might cost 0.10% to 0.50% or more. Over a 30-year career, the TSP's cost advantage can translate into tens of thousands of additional dollars at retirement.

The L Funds — Lifecycle Funds

The TSP also offers Lifecycle (L) funds, which are pre-mixed portfolios of the five individual funds. Each L Fund targets a specific retirement date and automatically adjusts its allocation over time, shifting from stocks toward bonds as the target date approaches.

The current L Fund lineup includes the L Income Fund (for those already withdrawing), and L 2030 through L 2070 in five-year increments. The L Funds follow a glide path — a predetermined schedule for shifting allocations. A younger participant's L Fund might hold 85% equities, while the L Income Fund holds roughly 74% in G and F Funds.

L Funds are convenient but offer no flexibility. If you want to overweight the S Fund during historically strong months or shift to the G Fund during expected downturns, you need to manage individual fund allocations yourself. The L Funds are designed for participants who prefer a completely hands-off approach.

Combining TSP Funds for Portfolio Construction

The art of TSP investing lies in how you combine the five individual funds. Here are several approaches, from simple to sophisticated:

The Simple Two-Fund Approach

Allocate between the C Fund (or a C/S blend for total market exposure) and the G Fund based on your risk tolerance. An aggressive investor might go 90% C Fund / 10% G Fund, while a conservative investor might choose 40% C Fund / 60% G Fund. This approach is easy to understand and maintain.

The Three-Fund Core

Combine the C Fund, S Fund, and I Fund to build a globally diversified equity portfolio, then add G or F Fund for stability. A common approach is to weight C and S in proportion to their market capitalization (roughly 80% C / 20% S for total U.S. market exposure) and add 20-30% in the I Fund for international diversification.

Seasonal Rotation

Rather than holding a static allocation, rotate among the five individual funds based on historical seasonal patterns. Different funds exhibit different seasonal tendencies — the C Fund may perform best in certain months, while the S Fund or I Fund leads in others. The G Fund serves as the defensive position during historically weak equity months.

Apex Equity's TSP alert system uses this approach, analyzing years of monthly TSP fund performance data to identify the optimal fund for each calendar month. The result is a simple, actionable monthly signal: which fund to hold for the upcoming month.

Risk-Based Allocation by Career Stage

Your TSP allocation should evolve as you progress through your career:

• Early career (20+ years to retirement): 80-100% equity funds (C, S, I). You have time to recover from downturns, so maximize growth potential.
• Mid-career (10-20 years to retirement): 60-80% equity funds, 20-40% G/F Funds. Begin adding stability without sacrificing too much growth.
• Near retirement (5-10 years): 40-60% equity funds, 40-60% G/F Funds. Protect accumulated wealth while maintaining some growth.
• In retirement: 20-40% equity funds, 60-80% G/F Funds. Prioritize capital preservation and income, keeping some equity exposure to combat inflation.

C Fund vs S Fund: The Great TSP Debate

The C Fund vs S Fund question deserves special attention because it is the most consequential allocation decision most TSP participants face. Here are the key considerations:

• Recent performance favors C Fund: Large-cap U.S. stocks (particularly technology mega-caps) have dominated the past decade. The C Fund has outperformed the S Fund in most recent years.
• Long-term history favors S Fund: Over multi-decade periods, small and mid-cap stocks have historically delivered a premium over large caps, consistent with the academic "size premium" research.
• Diversification argues for both: Holding both C and S in market-weight proportions (roughly 80/20) gives you total U.S. stock market exposure. This is the most diversified domestic equity approach.
• Rotation can capture the best of both: Rather than choosing one permanently, a seasonal rotation strategy can shift between C and S based on which fund's seasonal patterns are more favorable in a given month.

Key Takeaways for TSP Investors

• All five TSP funds serve distinct roles — understand what each one does before allocating your contributions.
• The G Fund is unique in offering guaranteed principal with intermediate-term yields — no other investment offers this combination.
• The C Fund and S Fund are highly correlated but not identical — combining them gives total U.S. market coverage.
• International diversification through the I Fund matters, even though U.S. stocks have led recently.
• TSP's ultra-low expense ratios are a massive advantage — do not underestimate the power of 0.05% fees over a career.
• Whether you choose a static allocation, lifecycle fund, or rotation strategy, the most important thing is to invest consistently and stay disciplined.

Frequently Asked Questions

Q: Which TSP fund has the highest returns?

A: Over the past decade, the C Fund (S&P 500) has delivered the highest returns, driven by large-cap technology stocks. Over longer periods, the S Fund (small/mid-cap) has historically offered slightly higher returns with more volatility.

Q: What is the safest TSP fund?

A: The G Fund is the safest — it is guaranteed by the U.S. government to never lose principal. It has posted positive returns every single year since 1987. The F Fund is the next safest but can lose value when interest rates rise.

Q: Should I invest in all 5 TSP funds?

A: Not necessarily. Most effective strategies use 2-4 funds. A simple C Fund + G Fund combination covers growth and safety. Adding the S Fund provides total market exposure. The I Fund adds international diversification. The F Fund is optional and most useful during falling rate environments.