VMCTX vs. POSKX

Last updated Jun 26, 2026

VMCTX (Vanguard Mega Cap Index Fund Institutional Shares) and POSKX (PrimeCap Odyssey Stock Fund) are both Large Cap Blend Equities funds. Over the past 10 years, VMCTX returned 16.32%/yr vs 17.00%/yr for POSKX. Their correlation of 0.92 suggests significant overlap in exposure. VMCTX charges 0.06%/yr vs 0.65%/yr for POSKX.

Performance

VMCTX vs. POSKX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in Vanguard Mega Cap Index Fund Institutional Shares (VMCTX) and PrimeCap Odyssey Stock Fund (POSKX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, VMCTX achieves a 7.20% return, which is significantly lower than POSKX's 24.66% return. Both investments have delivered pretty close results over the past 10 years, with VMCTX having a 16.32% annualized return and POSKX not far ahead at 17.00%.

VMCTX

• 1D: -0.26%
• 1M: -2.72%
• YTD: 7.20%
• 6M: 5.93%
• 1Y: 22.53%
• 3Y*: 21.84%
• 5Y*: 13.55%
• 10Y*: 16.32%

POSKX

• 1D: 0.12%
• 1M: 2.55%
• YTD: 24.66%
• 6M: 23.03%
• 1Y: 48.61%
• 3Y*: 25.15%
• 5Y*: 16.09%
• 10Y*: 17.00%

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

VMCTX vs. POSKX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
VMCTX Vanguard Mega Cap Index Fund Institutional Shares	7.20%	19.35%	27.18%	29.67%	-19.91%	27.57%	21.47%	31.42%	-3.47%	22.57%
POSKX PrimeCap Odyssey Stock Fund	24.66%	25.73%	12.77%	21.18%	-11.12%	32.48%	10.13%	27.15%	-7.19%	25.99%

Correlation

The correlation between VMCTX and POSKX is 0.77, which is moderate. They share some common price drivers but move independently often enough to provide real diversification benefit when combined.

	Correlation
Correlation (1Y) Calculated over the trailing 1-year period	0.77
Correlation (3Y) Calculated over the trailing 3-year period	0.82
Correlation (5Y) Calculated over the trailing 5-year period	0.87
Correlation (10Y) Calculated over the trailing 10-year period	0.88
Correlation (All Time) Calculated using the full available price history since Dec 27, 2007	0.92

The correlation between VMCTX and POSKX shifts across timeframes, from 0.77 (1 year) to 0.92 (all time), reflecting how their relationship changes across market environments.

Return for Risk

VMCTX vs. POSKX — Risk / Return Rank

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

VMCTX

VMCTX Risk / Return Rank: 51
VMCTX Sharpe Ratio Rank: 52
VMCTX Sortino Ratio Rank: 48
VMCTX Omega Ratio Rank: 49
VMCTX Calmar Ratio Rank: 48
VMCTX Martin Ratio Rank: 59

POSKX

POSKX Risk / Return Rank: 92
POSKX Sharpe Ratio Rank: 95
POSKX Sortino Ratio Rank: 91
POSKX Omega Ratio Rank: 86
POSKX Calmar Ratio Rank: 95
POSKX Martin Ratio Rank: 96

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.

VMCTX vs. POSKX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for Vanguard Mega Cap Index Fund Institutional Shares (VMCTX) and PrimeCap Odyssey Stock Fund (POSKX). 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.

Values are calculated on a 1-year rolling basis and updated daily. Risk-adjusted metrics are more stable over longer periods — use the period switch above to explore them.

	VMCTX	POSKX	Difference
Sharpe ratio: Return per unit of total volatility	1.75	2.88	-1.13
Sortino ratio: Return per unit of downside risk	2.40	3.96	-1.56
Omega ratio: Gain probability vs. loss probability	1.31	1.51	-0.19
Calmar ratio: Return relative to maximum drawdown	2.31	4.89	-2.58
Martin ratio: Return relative to average drawdown	9.95	20.24	-10.30

VMCTX vs. POSKX - Sharpe Ratio Comparison

The current VMCTX Sharpe Ratio is 1.75, which is lower than the POSKX Sharpe Ratio of 2.88. The chart below compares the historical Sharpe Ratios of VMCTX and POSKX, calculated using daily returns over the previous 12 months. A higher Sharpe Ratio indicates better risk-adjusted performance relative to the risk-free rate.

Drawdowns

VMCTX vs. POSKX - Drawdown Comparison

The maximum VMCTX drawdown since its inception was -52.00%, roughly equal to the maximum POSKX drawdown of -50.18%. Use the drawdown chart below to compare losses from any high point for VMCTX and POSKX.

Drawdown Indicators

	VMCTX	POSKX	Difference
Max Drawdown Largest peak-to-trough decline	-52.00%	-50.18%	-1.82%
Max Drawdown (1Y) Largest decline over 1 year	-9.87%	-9.99%	+0.12%
Max Drawdown (3Y) Largest decline over 3 years	-19.36%	-20.25%	+0.89%
Max Drawdown (5Y) Largest decline over 5 years	-25.77%	-22.96%	-2.81%
Max Drawdown (10Y) Largest decline over 10 years	-32.96%	-36.88%	+3.92%
Current Drawdown Current decline from peak	-4.02%	-1.69%	-2.33%
Average Drawdown Average peak-to-trough decline	-7.07%	-6.14%	-0.93%
Ulcer Index Depth and duration of drawdowns from previous peaks	2.29%	2.41%	-0.12%

Volatility

VMCTX vs. POSKX - Volatility Comparison

The current volatility for Vanguard Mega Cap Index Fund Institutional Shares (VMCTX) is 5.17%, while PrimeCap Odyssey Stock Fund (POSKX) has a volatility of 6.98%. This indicates that VMCTX experiences smaller price fluctuations and is considered to be less risky than POSKX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	VMCTX	POSKX	Difference
Volatility (1M) Calculated over the trailing 1-month period	5.17%	6.98%	-1.81%
Volatility (6M) Calculated over the trailing 6-month period	10.31%	13.95%	-3.64%
Volatility (1Y) Calculated over the trailing 1-year period	13.08%	17.01%	-3.93%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	17.46%	18.06%	-0.60%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	18.30%	19.04%	-0.74%

VMCTX vs. POSKX - Expense Ratio Comparison

VMCTX has a 0.06% expense ratio, which is lower than POSKX's 0.65% expense ratio.

Dividends

VMCTX vs. POSKX - Dividend Comparison

VMCTX's dividend yield for the trailing twelve months is around 0.91%, less than POSKX's 22.01% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
POSKX PrimeCap Odyssey Stock Fund	22.01%	27.44%	18.13%	10.14%	12.13%	14.58%	7.85%	6.03%	3.03%	2.17%	2.93%	1.92%
VMCTX Vanguard Mega Cap Index Fund Institutional Shares	0.91%	0.94%	1.16%	1.36%	1.66%	1.18%	1.46%	1.82%	2.11%	1.84%	2.13%	2.13%

Frequently Asked Questions

Can I hold both VMCTX and POSKX in my portfolio?

VMCTX and POSKX have a correlation of 0.77, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, VMCTX or POSKX?

POSKX has higher volatility (6.98%) compared to VMCTX (5.17%). In terms of maximum drawdown, VMCTX dropped -52.00% vs POSKX's -50.18%.

Which has better risk-adjusted returns?

POSKX currently has the higher Sharpe Ratio (2.88 vs 1.75), meaning it's delivered slightly more return per unit of risk over the trailing 12 months. However, this ranking shifts over time - use the Risk/Return Score above for a more comprehensive view that combines Sharpe, Sortino, and other measures used by quantitative funds.