TSP S Fund Strategy: Small Cap Investing for Maximum Growth

What is the TSP S Fund?

The S Fund (Small Cap Stock Index Investment Fund) tracks the Dow Jones U.S. Completion Total Stock Market Index. This fund invests in small and mid-cap U.S. companies — essentially every publicly traded stock not in the S&P 500.

While the C Fund gives you Apple, Microsoft, and Amazon, the S Fund gives you thousands of smaller, faster-growing companies that many investors overlook. These are the companies that could become tomorrow's blue chips.

S Fund Key Facts:

• Benchmark: Dow Jones U.S. Completion Total Stock Market Index
• Holdings: ~3,400 small and mid-cap stocks
• Expense Ratio: ~0.05%
• Historical Average Return: ~10-12% annually over 20 years
• Risk Level: High (more volatile than C Fund)
• Best for: Growth-oriented investors with long time horizons

S Fund vs. C Fund: When Does Small Cap Win?

The most common question about the S Fund: is it better than the C Fund? The answer depends on timing and market cycles.

When the S Fund Outperforms:

• Early economic recoveries: Small caps typically surge coming out of recessions. After the 2009 bottom and 2020 COVID crash, the S Fund dramatically outperformed the C Fund.
• Broadening economic growth: Small caps benefit when economic growth extends beyond large corporations to smaller businesses.
• Periods of broadening market participation: When the rally extends beyond mega-cap tech stocks.

When the C Fund Outperforms:

• Late-cycle bull markets: Money flows to quality large caps during uncertain times.
• Tech-driven rallies: When a handful of mega-cap tech stocks drive most of the market's returns (like 2023-2024).
• Flight to quality: During market stress, large caps are more resilient.

Over very long periods (20+ years), the S Fund and C Fund have delivered similar total returns, but with different timing. This makes combining them a powerful diversification strategy.

Strategy 1: The Growth Maximizer (100% S Fund)

Going 100% S Fund is the most aggressive TSP strategy available. Small caps have higher volatility but also higher potential returns — especially during economic recoveries.

Historical Performance Highlights:

• 2003: S Fund returned +42.9% (vs. C Fund +28.5%)
• 2009: S Fund returned +34.9% (vs. C Fund +26.7%)
• 2020 recovery: S Fund surged from March lows, dramatically outpacing C Fund

The risk: The S Fund also falls harder during crashes. In 2008, the S Fund dropped -38.3% compared to the C Fund's -36.9%. And in extended downturns, small caps can underperform for years.

Best for: Young, aggressive investors (under 30) with 30+ years until retirement and iron stomachs.

Strategy 2: Total Market (80% C Fund / 20% S Fund)

This is the most academically sound allocation. An 80/20 C/S split roughly mirrors the total U.S. stock market by market capitalization. A 50/50 split overweights small caps for potentially higher growth. You get:

• Full market exposure: Large caps, mid caps, and small caps
• Automatic rebalancing benefit: When one segment outperforms, rebalancing forces you to buy low and sell high
• Slightly higher expected returns: The small cap premium has been well-documented in academic finance

This strategy requires annual rebalancing to maintain the 80/20 ratio. Set a calendar reminder to check and adjust once per year.

Strategy 3: S Fund Seasonality Timing

Small caps have even more pronounced seasonal patterns than large caps, making the S Fund particularly well-suited for seasonality strategies.

Key S Fund Seasonal Patterns:

• January Effect: Small caps historically surge in January as investors buy beaten-down stocks after year-end tax-loss selling
• November-February: The strongest seasonal window for small caps
• May-September: "Sell in May" hits small caps harder than large caps
• October: Often marks the seasonal bottom for small caps

A seasonality strategy that rotates between the S Fund (during strong months) and G Fund (during weak months) has shown backtested results of 18-28% CAGR — significantly outperforming buy-and-hold.

View our TSP seasonality strategies to see how S Fund timing works in practice.

Strategy 4: S Fund for Recovery Plays

One of the most powerful S Fund strategies is increasing your allocation after major market drops. Historically:

• After major market declines, small caps have historically tended to outperform large caps during the recovery period
• After the 2020 COVID crash, the S Fund returned +80% from the March low to year-end (vs. C Fund +65%)
• After the 2008-2009 bottom, the S Fund returned +82% in the first 12 months of recovery

This "crash recovery" approach: stay in C Fund or balanced allocation normally, then shift heavily to S Fund after a 20%+ market decline. Simple, powerful, and backed by decades of data.

S Fund Allocation by Career Stage

Early Career (Under 35):

50-100% S Fund. You have decades to compound and can absorb volatility. The small cap premium works best over long horizons.

Mid Career (35-50):

30-50% S Fund combined with C Fund and small G Fund allocation. You still want growth but need some stability.

Pre-Retirement (50+):

10-20% S Fund as a growth kicker alongside a more conservative C/G/F allocation. Small caps add diversification even in conservative portfolios.

Common S Fund Mistakes

1. Abandoning S Fund after underperformance: Small caps go through multi-year periods of underperformance, then roar back. Selling after the down period means missing the recovery.
2. Ignoring the S Fund entirely: Many TSP participants only use C Fund and G Fund, missing out on small cap diversification.
3. Over-concentrating after a good year: Going 100% S Fund after it surges 40% is chasing performance. Stick to your strategy.
4. Not understanding the volatility: S Fund can swing 3-5% in a week. If daily fluctuations stress you out, reduce your allocation.

Getting Started with Your S Fund Strategy

Ready to put the S Fund to work? Here's how:

1. Review your current allocation at tsp.gov
2. Decide on your target S Fund percentage based on your career stage and risk tolerance
3. Make an interfund transfer to set your new allocation
4. Update your contribution allocation so new money flows to your target split
5. Consider a seasonality approach — subscribe to our TSP alerts for data-driven timing signals

The S Fund is one of the TSP's most powerful tools for building wealth. Used correctly — whether through buy-and-hold, seasonal timing, or recovery plays — it can significantly boost your retirement savings over a full career.