VFFSX vs. RCKSX

Last updated Apr 2, 2026

Compare and contrast key facts about Vanguard 500 Index Fund Institutional Select Shares (VFFSX) and Rock Oak Core Growth Fund (RCKSX).

VFFSX is managed by Vanguard. RCKSX is managed by Oak Associates. It was launched on Dec 31, 2004.

Performance

VFFSX vs. RCKSX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in Vanguard 500 Index Fund Institutional Select Shares (VFFSX) and Rock Oak Core Growth Fund (RCKSX). The values are adjusted to include any dividend payments, if applicable.

VFFSX vs. RCKSX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
VFFSX Vanguard 500 Index Fund Institutional Select Shares	-4.34%	17.87%	25.00%	26.28%	-18.14%	29.24%	18.35%	31.88%	-4.42%	20.80%
RCKSX Rock Oak Core Growth Fund	7.71%	12.99%	15.12%	15.57%	-18.09%	9.96%	13.75%	19.05%	-2.14%	21.60%

Returns By Period

In the year-to-date period, VFFSX achieves a -4.34% return, which is significantly lower than RCKSX's 7.71% return.

VFFSX

• 1D: 2.92%
• 1M: -5.03%
• YTD: -4.34%
• 6M: -2.14%
• 1Y: 17.34%
• 3Y*: 18.30%
• 5Y*: 11.78%
• 10Y*: —

RCKSX

• 1D: 1.56%
• 1M: -1.74%
• YTD: 7.71%
• 6M: 8.21%
• 1Y: 22.14%
• 3Y*: 17.13%
• 5Y*: 5.93%
• 10Y*: 10.38%

*Multi-year figures are annualized to reflect compound growth (CAGR)

VFFSX vs. RCKSX - Expense Ratio Comparison

VFFSX has a 0.01% expense ratio, which is lower than RCKSX's 1.25% expense ratio.

RCKSX

Rock Oak Core Growth Fund

VFFSX

Vanguard 500 Index Fund Institutional Select Shares

Return for Risk

VFFSX vs. RCKSX — Risk / Return Rank

Compare risk-adjusted metric ranks to identify better-performing investments over the past 12 months.

VFFSX

VFFSX Risk / Return Rank: 59
VFFSX Sharpe Ratio Rank: 48
VFFSX Sortino Ratio Rank: 53
VFFSX Omega Ratio Rank: 56
VFFSX Calmar Ratio Rank: 64
VFFSX Martin Ratio Rank: 76

RCKSX

RCKSX Risk / Return Rank: 77
RCKSX Sharpe Ratio Rank: 73
RCKSX Sortino Ratio Rank: 77
RCKSX Omega Ratio Rank: 68
RCKSX Calmar Ratio Rank: 80
RCKSX Martin Ratio Rank: 90

The rank (0–100) shows how this investment's returns compare to the risk taken. Higher = better. Based on the past 12 months of data, combining Sharpe, Sortino, and other metrics used by quantitative funds and institutional investors.

VFFSX vs. RCKSX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for Vanguard 500 Index Fund Institutional Select Shares (VFFSX) and Rock Oak Core Growth Fund (RCKSX). Risk-adjusted metrics are performance indicators that assess an investment's returns in relation to its risk, enabling a more accurate comparison of different investment options.

	VFFSX	RCKSX	Difference
Sharpe ratio Return per unit of total volatility	0.98	1.40	-0.43
Sortino ratio Return per unit of downside risk	1.49	2.06	-0.57
Omega ratio Gain probability vs. loss probability	1.23	1.28	-0.05
Calmar ratio Return relative to maximum drawdown	1.52	2.09	-0.56
Martin ratio Return relative to average drawdown	7.31	10.93	-3.62
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

VFFSX vs. RCKSX - Sharpe Ratio Comparison

The current VFFSX Sharpe Ratio is 0.98, which is lower than the RCKSX Sharpe Ratio of 1.40. The chart below compares the historical Sharpe Ratios of VFFSX and RCKSX, offering insights into how both investments have performed under varying market conditions. These values are calculated using daily returns over the previous 12 months.

Sharpe Ratios by Period

	VFFSX	RCKSX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	0.98	1.40	-0.43
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.70	0.38	+0.32
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	—	0.59	—
Sharpe Ratio (All Time) Calculated using the full available price history	0.77	0.37	+0.40

Correlation

The correlation between VFFSX and RCKSX is 0.85, which is considered to be high. That indicates a strong positive relationship between their price movements. Having highly-correlated positions in a portfolio may signal a lack of diversification, potentially leading to increased risk during market downturns.

Dividends

VFFSX vs. RCKSX - Dividend Comparison

VFFSX's dividend yield for the trailing twelve months is around 1.21%, less than RCKSX's 5.81% yield.

	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
VFFSX Vanguard 500 Index Fund Institutional Select Shares	1.21%	1.14%	1.24%	1.46%	1.70%	1.61%	1.56%	2.15%	2.09%	1.81%	0.00%	0.00%
RCKSX Rock Oak Core Growth Fund	5.81%	6.26%	0.47%	0.71%	1.00%	4.31%	16.56%	3.18%	0.59%	5.91%	0.70%	3.21%

Drawdowns

VFFSX vs. RCKSX - Drawdown Comparison

The maximum VFFSX drawdown since its inception was -33.82%, smaller than the maximum RCKSX drawdown of -57.88%. Use the drawdown chart below to compare losses from any high point for VFFSX and RCKSX.

Drawdown Indicators

	VFFSX	RCKSX	Difference
Max Drawdown Largest peak-to-trough decline	-33.82%	-57.88%	+24.06%
Max Drawdown (1Y) Largest decline over 1 year	-12.12%	-11.29%	-0.83%
Max Drawdown (5Y) Largest decline over 5 years	-24.51%	-23.50%	-1.01%
Max Drawdown (10Y) Largest decline over 10 years	—	-33.10%	—
Current Drawdown Current decline from peak	-6.24%	-1.74%	-4.50%
Average Drawdown Average peak-to-trough decline	-4.57%	-9.58%	+5.01%
Ulcer Index Depth and duration of drawdowns from previous peaks	2.52%	2.16%	+0.36%

Volatility

VFFSX vs. RCKSX - Volatility Comparison

Vanguard 500 Index Fund Institutional Select Shares (VFFSX) has a higher volatility of 5.35% compared to Rock Oak Core Growth Fund (RCKSX) at 3.72%. This indicates that VFFSX's price experiences larger fluctuations and is considered to be riskier than RCKSX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	VFFSX	RCKSX	Difference
Volatility (1M) Calculated over the trailing 1-month period	5.35%	3.72%	+1.63%
Volatility (6M) Calculated over the trailing 6-month period	9.53%	8.88%	+0.65%
Volatility (1Y) Calculated over the trailing 1-year period	18.32%	16.40%	+1.92%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	16.91%	15.78%	+1.13%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	18.52%	17.59%	+0.93%