TSP Fund Pairing Insights: Navigating Risk and Returns

31 May 2026

Executive Takeaway

The May 2026 TSP risk backdrop is Neutral, not because risk is absent, but because volatility and diversification signals are moving in opposite directions. Equity returns remained strongly positive, with C Fund up 5.26%, I Fund up 4.90%, and S Fund up 4.49%, but those gains were meaningfully weaker than April’s 9.11%–10.49% equity surge. The dominant volatility signal is S Fund 12-month volatility rising 6.01%, while the dominant equity–equity diversification signal is C/I covariance falling 7.41% tactically and 28.88% structurally, creating a mixed but not risk-off environment.

Visualization for 31 May 2026

X-Axis:

Represents the “risk” of the particular mix, measured by statistical covariance over the last three years of monthly data. Left to right: From less variable (lower risk) to more variable (higher risk).

Y-Axis:

Represents the statistical “expected monthly return” of the particular mix, measured by the mean of the last three years of monthly data. Bottom to top: From lower returns to higher returns.

Legend:

Each line represents a specific fund mix (e.g., G and F Fund). The line shows how the risk and return evolve as the mix transitions from 100% of one fund to 100% of the other in 5% increments.

Market Context (Prices & Returns)

May remained a growth-positive month, but the force of the advance cooled materially from April.

The equity funds all posted strong gains:

Fund	May Return	April Return	Change in Return Momentum
C Fund	5.26%	10.49%	Down 5.23 percentage points
S Fund	4.49%	9.96%	Down 5.47 percentage points
I Fund	4.90%	9.11%	Down 4.21 percentage points
G Fund	0.39%	0.36%	Up 0.03 percentage points
F Fund	0.33%	0.12%	Up 0.21 percentage points

Return dispersion across equities narrowed sharply. In April, the spread between the best and weakest equity fund was 1.38 percentage points: C Fund at 10.49% versus I Fund at 9.11%. In May, the equity spread narrowed to 0.77 percentage points: C Fund at 5.26% versus S Fund at 4.49%.

That narrowing matters. It means May was not a market where one equity segment dramatically separated from the others. Growth exposure broadly worked, but with less leadership dispersion and less return acceleration than April.

From the defensive lens, the G and F Funds provided modest positive returns of 0.39% and 0.33%, but they materially lagged equities by roughly 4.10 to 4.93 percentage points. From the growth lens, equities still dominated returns, but the slowdown from April argues against treating May as a clean risk-on acceleration.

Volatility Signals (12-Month vs 24-Month)

12-Month Volatility (Tactical)

12-Month Tactical Volatility

The 12-month volatility signal is mildly risk-expansive, led by small-cap volatility.

Fund	12M Volatility Change	Direction
C Fund	+2.19%	Remained / slight rise
S Fund	+6.01%	Rose
I Fund	+0.07%	Remained
G Fund	-16.02%	Fell
F Fund	+5.65%	Rose

The dominant equity volatility signal is the S Fund’s +6.01% increase, the largest absolute percentage change among the equity funds. That matters because the S Fund often represents the more volatility-sensitive portion of the TSP equity complex. A 6.01% tactical rise in S Fund volatility means the equity risk environment became less calm at the margin, even though C Fund and I Fund changes were much smaller at +2.19% and +0.07%.

However, this is not a broad volatility breakout. Only one of the three equity funds clearly rose in 12-month volatility. C Fund and I Fund were classified as “Remained,” not “Rose.”

24-Month Volatility (Structural)

The 24-month signals lean slightly in the opposite direction.

Fund	24M Volatility Change	Direction
C Fund	-0.35%	Remained
S Fund	-0.48%	Remained
I Fund	-0.03%	Remained
G Fund	+8.90%	Rose
F Fund	+2.13%	Remained

Structurally, all three equity funds show tiny volatility declines: C Fund -0.35%, S Fund -0.48%, and I Fund -0.03%. These are not large enough to declare a structural risk improvement, but they do prevent the tactical S Fund volatility rise from dominating the entire regime classification.

The tactical and structural signals conflict most clearly in the S Fund: +6.01% on the 12-month horizon versus -0.48% on the 24-month horizon. That divergence supports a Neutral classification because the tactical rise is not structurally confirmed.

Historical percentile note: only percentiles below the 10th percentile are regime-relevant here. S Fund 12-month volatility sits at the 1.43rd percentile, F Fund 12-month volatility at 7.05th percentile, G Fund 24-month volatility at 7.13th percentile, and F Fund 24-month volatility at 3.87th percentile. The S Fund’s extremely low percentile makes the +6.01% rise more important: it may represent early normalization from unusually suppressed volatility rather than a full risk-off break.

Diversification Signals (Covariance)

The covariance backdrop is more constructive than the volatility backdrop.

12-Month Equity Covariance (Tactical)

Pair	12M Covariance Change	Direction
C/S Pair	-7.02%	Fell
C/I Pair	-7.41%	Fell
S/I Pair	-6.54%	Fell

All three primary equity covariance pairs declined tactically. The largest equity–equity covariance change is the C/I Pair at -7.41%, narrowly exceeding C/S at -7.02% and S/I at -6.54%.

That is a material diversification improvement, but not a dramatic one. The signal is directionally consistent across all three equity pairs, yet the magnitude is below the >30% threshold required to serve as strong Risk-On confirmation.

24-Month Equity Covariance (Structural)

Pair	24M Covariance Change	Direction
C/S Pair	-12.29%	Fell
C/I Pair	-28.88%	Fell
S/I Pair	-15.53%	Fell

The structural covariance picture is also constructive. Again, all three equity–equity covariance pairs declined, with the largest decline in the C/I Pair at -28.88%.

This matters because tactical diversification improvement is being reinforced structurally, especially in the C/I relationship. However, the largest structural decline of -28.88% remains just short of the >30% threshold that would provide stronger Risk-On confirmation.

Using the required diversification rule: equity–equity diversification is Improving because the largest changes are declines, all three primary pairs fell, and there are no offsetting increases among the primary equity pairs.

Portfolio Risk Regime Assessment

The final classification is Neutral.

Signal Sequence

1. Volatility assessment:
The dominant equity volatility signal is the S Fund’s +6.01% 12-month volatility increase. That points to mild tactical risk expansion. But C Fund rose only 2.19%, I Fund was nearly flat at +0.07%, and the 24-month equity volatility changes were slightly negative across all three equity funds: C -0.35%, S -0.48%, I -0.03%. This means volatility does not show broad alignment.

2. Diversification assessment:
The dominant equity–equity diversification signal is the C/I covariance decline, falling 7.41% over 12 months and 28.88% over 24 months. All three equity–equity covariance pairs declined across both horizons, making diversification the strongest constructive signal in the data.

3. Conflict resolution:
Volatility and diversification conflict. Tactical equity volatility is rising selectively, led by S Fund at +6.01%, while equity–equity covariance is improving across the board, led by C/I at -7.41% tactically and -28.88% structurally. Under the required rule, conflicting signals default to Neutral unless 24-month signals reinforce one side with at least 2× magnitude versus the opposing signal. The 24-month C/I covariance decline of -28.88% is constructive, but it does not convert the whole regime to Risk-On because the Risk-On definition also requires either 24-month volatility confirmation or a majority of equity–equity covariance declines greater than 30%. The covariance declines are broad, but not above that threshold.

Why Neutral, Not Risk-On
Risk-On is not selected because the volatility condition is not met. Risk-On requires at least two equity funds showing declining 12-month volatility. Instead, C Fund is +2.19%, S Fund is +6.01%, and I Fund is +0.07%. None of the three equity funds show a 12-month volatility decline.

The covariance side is constructive, but not strong enough to override this. All three equity–equity covariance pairs declined, but the 12-month declines are only -7.02%, -7.41%, and -6.54%, below the >30% majority threshold.

Why Neutral, Not Risk-Off
Risk-Off is not selected because the risk-expansion signal is not broad enough. Risk-Off requires at least two equity funds showing rising volatility, or largest-magnitude equity–equity covariance increases showing diversification deterioration. Here, only S Fund clearly rose in 12-month volatility at +6.01%. C and I were classified as “Remained.”

More importantly, the largest equity–equity covariance changes are declines, not increases. C/I covariance fell -7.41% over 12 months and -28.88% over 24 months. That points to improving diversification, not deterioration.

Risk Driver Attribution

Risk containment is being driven mainly by diversification effects, because all three equity–equity covariance pairs declined tactically and structurally, including C/I at -7.41% over 12 months and -28.88% over 24 months.

Risk expansion is being driven mainly by equity volatility behavior, specifically the S Fund’s +6.01% 12-month volatility increase. That is the clearest tactical warning signal.

Defensive asset dampening is mixed. G Fund 12-month volatility fell 16.02%, which supports capital preservation, but F Fund 12-month volatility rose 5.65%, limiting the defensive complex’s consistency. The defensive sleeve is therefore helpful, but not uniformly dampening.

Synthesis
The portfolio risk environment is balanced between mild volatility expansion and improving diversification. The S Fund’s +6.01% 12-month volatility increase argues against aggressive risk expansion, but the C/I covariance decline of -7.41% tactically and -28.88% structurally argues against de-risking too aggressively. As a result, the risk environment leaves the portfolio risk budget appropriately utilized, not clearly under-utilized or stretched.

Recommendation

The recommendation is conditional neutrality: stay selective, avoid chasing May’s equity strength, and use rebalancing rather than broad directional allocation changes.

For Defensive / Capital Preservation portfolios, the signal set supports patience and risk control. The S Fund’s +6.01% 12-month volatility rise is enough to avoid aggressive equity expansion, especially since the 12-month equity volatility picture is not broadly declining. Defensive investors should treat the improved covariance backdrop as helpful, but not as permission to materially increase risk.

For Growth / Risk-Seeking portfolios, the data does not argue for retreat. Equity returns remained strong, with C Fund +5.26%, I Fund +4.90%, and S Fund +4.49%, while all three equity–equity covariance pairs declined tactically. Growth investors can remain engaged, but should be selective because the volatility signal is not cleanly Risk-On and April-to-May return momentum cooled by more than 4 percentage points across all three equity funds.

Bottom line: this is a Neutral regime where rebalancing and selectivity are favored over major risk expansion or defensive retreat.

Watchlist for Next Month

1. If at least two of C, S, and I show 12-month volatility declines greater than 2%, then a Risk-On regime becomes more likely, especially if equity–equity covariance remains negative across C/S, C/I, and S/I.
2. If S Fund 12-month volatility rises another 5% or more and either C Fund or I Fund also shifts from “Remained” to “Rose,” then Risk-Off becomes more likely, because equity volatility expansion would become broad rather than isolated.
3. If the C/I 24-month covariance decline crosses below -30% and at least two 12-month equity–equity covariance pairs decline by more than 30%, then Risk-On becomes more likely, because diversification improvement would meet the structural confirmation threshold.

More to follow next month…

Disclaimer