MGK vs. SPAXX

Last updated Jun 9, 2026

MGK (Vanguard Mega Cap Growth ETF) and SPAXX (Fidelity Government Money Market Fund) are both funds - MGK is a Large Cap Growth Equities fund tracking the CRSP US Mega Cap Growth Index, while SPAXX is a Money Market fund actively managed by Fidelity. MGK is passively managed, while SPAXX is actively managed. Over the past 5 years, MGK returned 15.44%/yr vs 1.45%/yr for SPAXX. At a 0.00 correlation, their price movements are largely independent. MGK charges 0.05%/yr vs 0.42%/yr for SPAXX.

Performance

MGK vs. SPAXX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in Vanguard Mega Cap Growth ETF (MGK) and Fidelity Government Money Market Fund (SPAXX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, MGK achieves a 6.52% return, which is significantly higher than SPAXX's 1.37% return.

MGK

• 1D: 0.45%
• 1M: -0.30%
• YTD: 6.52%
• 6M: 5.59%
• 1Y: 25.21%
• 3Y*: 25.50%
• 5Y*: 15.44%
• 10Y*: 18.91%

SPAXX

• 1D: 0.00%
• 1M: 0.28%
• YTD: 1.37%
• 6M: 1.67%
• 1Y: 3.66%
• 3Y*: 2.42%
• 5Y*: 1.45%
• 10Y*: —

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

MGK vs. SPAXX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021
MGK Vanguard Mega Cap Growth ETF	6.52%	20.67%	32.94%	51.67%	-33.59%	19.88%
SPAXX Fidelity Government Money Market Fund	1.37%	3.96%	1.54%	0.41%	0.00%	0.00%

Correlation

The correlation between MGK and SPAXX is -0.01, meaning there is essentially no relationship between their price movements. Each responds to its own set of market drivers, making them strong candidates for combining in a diversified portfolio.

	Correlation
Correlation (1Y) Calculated over the trailing 1-year period	-0.01
Correlation (3Y) Calculated over the trailing 3-year period	-0.00
Correlation (5Y) Calculated over the trailing 5-year period	0.00
Correlation (All Time) Calculated using the full available price history since May 26, 2021	0.00

Return for Risk

MGK vs. SPAXX — Risk / Return Rank

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

MGK

MGK Risk / Return Rank: 42
MGK Sharpe Ratio Rank: 48
MGK Sortino Ratio Rank: 47
MGK Omega Ratio Rank: 47
MGK Calmar Ratio Rank: 34
MGK Martin Ratio Rank: 36

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.

MGK vs. SPAXX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for Vanguard Mega Cap Growth ETF (MGK) and Fidelity Government Money Market Fund (SPAXX). 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.

	MGK	SPAXX	Difference
Sharpe ratio: Return per unit of total volatility	1.52	3.65	-2.12
Sortino ratio: Return per unit of downside risk	2.08	—	—
Omega ratio: Gain probability vs. loss probability	1.27	—	—
Calmar ratio: Return relative to maximum drawdown	1.50	—	—
Martin ratio: Return relative to average drawdown	5.15	—	—
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

MGK vs. SPAXX - Sharpe Ratio Comparison

The current MGK Sharpe Ratio is 1.52, which is lower than the SPAXX Sharpe Ratio of 3.65. The chart below compares the historical Sharpe Ratios of MGK and SPAXX, calculated using daily returns over the previous 12 months. A higher Sharpe Ratio indicates better risk-adjusted performance relative to the risk-free rate.

Sharpe Ratios by Period

	MGK	SPAXX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	1.52	3.65	-2.12
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.68	2.13	-1.45
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	0.87	—	—
Sharpe Ratio (All Time) Calculated using the full available price history	0.65	2.12	-1.48

Drawdowns

MGK vs. SPAXX - Drawdown Comparison

The maximum MGK drawdown since its inception was -47.97%, which is greater than SPAXX's maximum drawdown of 0.00%. Use the drawdown chart below to compare losses from any high point for MGK and SPAXX.

Drawdown Indicators

	MGK	SPAXX	Difference
Max Drawdown Largest peak-to-trough decline	-47.97%	0.00%	-47.97%
Max Drawdown (1Y) Largest decline over 1 year	-16.85%	0.00%	-16.85%
Max Drawdown (3Y) Largest decline over 3 years	-23.36%	0.00%	-23.36%
Max Drawdown (5Y) Largest decline over 5 years	-36.01%	0.00%	-36.01%
Max Drawdown (10Y) Largest decline over 10 years	-36.01%	—	—
Current Drawdown Current decline from peak	-4.56%	0.00%	-4.56%
Average Drawdown Average peak-to-trough decline	-7.47%	0.00%	-7.47%
Ulcer Index Depth and duration of drawdowns from previous peaks	4.91%	0.00%	+4.91%

Volatility

MGK vs. SPAXX - Volatility Comparison

Vanguard Mega Cap Growth ETF (MGK) has a higher volatility of 5.41% compared to Fidelity Government Money Market Fund (SPAXX) at 0.28%. This indicates that MGK's price experiences larger fluctuations and is considered to be riskier than SPAXX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	MGK	SPAXX	Difference
Volatility (1M) Calculated over the trailing 1-month period	5.41%	0.28%	+5.13%
Volatility (6M) Calculated over the trailing 6-month period	12.96%	0.72%	+12.24%
Volatility (1Y) Calculated over the trailing 1-year period	16.65%	1.03%	+15.62%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	22.69%	0.69%	+22.00%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	21.92%	0.69%	+21.23%

MGK vs. SPAXX - Expense Ratio Comparison

MGK has a 0.05% expense ratio, which is lower than SPAXX's 0.42% expense ratio.

Dividends

MGK vs. SPAXX - Dividend Comparison

MGK's dividend yield for the trailing twelve months is around 0.33%, less than SPAXX's 3.59% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
MGK Vanguard Mega Cap Growth ETF	0.33%	0.35%	0.43%	0.50%	0.70%	0.41%	0.65%	0.85%	1.12%	1.23%	1.53%	1.43%
SPAXX Fidelity Government Money Market Fund	3.59%	3.88%	1.53%	0.41%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%

Frequently Asked Questions

Can I hold both MGK and SPAXX in my portfolio?

MGK and SPAXX have a correlation of -0.01, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, MGK or SPAXX?

MGK has higher volatility (5.41%) compared to SPAXX (0.28%). In terms of maximum drawdown, MGK dropped -47.97% vs SPAXX's 0.00%.

Which has better risk-adjusted returns?

SPAXX currently has the higher Sharpe Ratio (3.65 vs 1.52), 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.