TSP Performance Strong in May: I Fund Leads 2026 at 16.56%
TSP Performance Strong in May: I Fund Leads 2026 at 16.56%
By Ralph R. Smith
TSP performance in May was strong, again contrary to the "sell in May, then go away" philosophy for some stock traders. Here is an analysis of the latest TSP returns.
The backdrop for Thrift Savings Plan (TSP) investors leading into May 2026 was unsettled. But, despite political and economic uncertainty, there is a positive return for all TSP funds for May.
The S&P 500 hit a new all-time high on May 1, and earnings season came in strong. The old stock traders’ philosophy, “sell in May, then go away,” failed — again — to materialize.
For TSP investors, the result was another solid month across the board with positive TSP returns. The C Fund gained 5.26%, the S Fund added 4.49%, and the I Fund climbed 4.90%. Every active TSP fund posted a positive return for May.
Year-to-date, the numbers are striking: the C Fund is up 11.26%, the S Fund is up 13.48%, and the I Fund leads all options at 16.56% — a figure that would have looked ambitious at the start of the year. This is the second consecutive year that May has delivered well-above-average returns for the core stock funds.
According to the Federal Retirement Thrift Investment Board (FRTIB), the average TSP account balance for FERS participants stood at $226,251 as of April 30, 2026. The total average balance across all 7.3 million TSP accounts was $152,847. CSRS participants carried the highest average at $249,511, reflecting longer tenures and greater accumulation. Those figures do not yet reflect May’s gains; with the core stock funds up between 4.49% and 5.26% for the month, current balances are likely now meaningfully higher.
C Fund: Earnings Drive Another Solid Month
The S&P 500 index (the index on which the TSP’s C Fund is based) hit a new all-time intraday high on May 1, and it built on that strength throughout most of the month. The C Fund’s 5.26% gain reflects a market that largely ignored the geopolitical background noise and focused on fundamentals.
- Approximately 78% of S&P 500 companies reporting for the first quarter beat consensus earnings estimates — well above the 10-year average of 74%. That earnings strength was the primary fuel for May’s advance.
- Despite higher oil prices and mid-month bond market volatility, investor sentiment remained positive.
- The 12-month trailing return of 29.76% for the C Fund reflects one of the fund’s strongest rolling 12-month periods in the past decade.
Outlook: Earnings momentum continues to drive stock prices higher, as reflected in TSP results for 2026 so far. The risks for investors are real, though: inflation is above 3%, the Fed Reserve’s reluctance to cut rates, and the potential for the Iran conflict to escalate or disrupt supply chains still exists. Stock prices reflect an optimistic scenario; any deterioration could prompt a pullback.
S Fund: Solid Gains, Still Behind on the Month
Small- and mid-cap U.S. stocks also went up, although the S Fund slightly trailed both the C Fund and the I Fund for the month.
- Despite trailing in May, the S Fund leads the C Fund year-to-date at 13.48% versus 11.26% — a gap built primarily in earlier months of 2026.
- Small-cap performance tends to be more sensitive to domestic interest rate expectations. The prospect of rates staying higher for a longer time is a headwind for this Fund.
- The S Fund’s 12-month trailing return of 30.48% actually edges out the C Fund’s over this longer term.
- Energy and defense companies in the small-cap universe have benefited from the war in Iran.
12-Month Performance Comparison: C Fund vs. S Fund
| FUND | START PRICE | END PRICE | TOTAL RETURN | ANNUALIZED |
|---|---|---|---|---|
| C Fund | $93.9035 | $121.8470 | +29.76% | +29.87% |
| S Fund | $87.3322 | $113.9473 | +30.48% | +30.59% |
I Fund: The Year’s Clear Leader
The I Fund has built a commanding lead for 2026, and May extended it. At a 16.56% return so far this year, the I Fund leads every other TSP option by a wide margin.
- Two forces are at work: solid international equity market performance and continued U.S. dollar weakness. When the dollar falls, overseas gains convert back into more dollars — amplifying returns for dollar-based investors.
- The 12-month return of 34.93% for this Fund is exceptional. It is among the highest rolling 12-month figures the I Fund has posted in recent years.
- TSP participants considering adding more of their investment dollars into this Fund need to be aware of the currency component: the dollar tailwind that has helped in 2026 can reverse, and currencies can move quickly.
Outlook: The I Fund’s fortunes remain closely tied to the dollar. Relative valuations of non-U.S. equities are more modest than U.S. counterparts, which provides a fundamental argument for international exposure. But a dollar stabilization or reversal would reduce the currency-amplified returns that have been a key part of the story this year.
TSP Performance for May 2026, Year-to-Date and 12-Month Returns
Historical Context
May 2026 ranks as an exceptional month by historical standards. The C Fund’s 5.26% gain is the 6th best May return in the fund’s 38-year history — well above its 10-year same-month average of 1.47% (2016–2025).
The I Fund’s 4.90% return is the 4th best May on record in its 25-year history, trailing only 2009 (13.41%), 2003 (6.07%), and 2025 (4.97%). The I Fund has now posted May returns between 4.86% and 4.97% for three consecutive years — 2024, 2025, and 2026.
The C Fund has also strung together four consecutive positive Mays (2023–2026), a run that stands in contrast to the sharp May losses of 2019 (−6.36%) and 2010 (−7.99%). All three core stock funds delivered May returns more than three times their respective 10-year averages.
Where Do We Go From Here?
No one knows what unexpected events will occur. The Iran war, which has already reshaped energy markets and kept inflation above the Fed’s target, could escalate or move toward a resolution. Either outcome would ripple across the TSP funds. Here is a look at what may lie ahead to help TSP investors in their investment and retirement planning.
C Fund
The earnings backdrop supports stock prices heading into summer. Roughly 78% of companies beat first-quarter estimates. The risks are real, however: the inflation index watched by the Federal Reserve is running above 3% annually. It has essentially signaled that it will not cut rates amid this uncertainty, and markets are pricing in a probability of an interest rate hike later this year. The S&P 500 is trading at elevated valuations relative to historical norms. That does not mean a decline in prices is imminent, but it does suggest that strong returns like May’s may not be the default scenario going forward.