STMGX vs. FMDGX

Last updated Jun 4, 2026

STMGX (American Beacon Stephens Mid-Cap Growth Fund) and FMDGX (Fidelity Mid Cap Growth Index Fund) are both Mid Cap Growth Equities funds. Over the past 5 years, STMGX returned 7.34%/yr vs 7.23%/yr for FMDGX. With a 0.96 correlation, they move nearly in lockstep. STMGX charges 1.14%/yr vs 0.05%/yr for FMDGX.

Performance

STMGX vs. FMDGX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in American Beacon Stephens Mid-Cap Growth Fund (STMGX) and Fidelity Mid Cap Growth Index Fund (FMDGX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, STMGX achieves a 11.65% return, which is significantly higher than FMDGX's 4.88% return.

STMGX

• 1D: 0.71%
• 1M: 8.63%
• YTD: 11.65%
• 6M: 10.19%
• 1Y: 21.54%
• 3Y*: 17.25%
• 5Y*: 7.34%
• 10Y*: 13.85%

FMDGX

• 1D: -0.22%
• 1M: 5.21%
• YTD: 4.88%
• 6M: 3.96%
• 1Y: 6.81%
• 3Y*: 16.42%
• 5Y*: 7.23%
• 10Y*: —

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

STMGX vs. FMDGX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019
STMGX American Beacon Stephens Mid-Cap Growth Fund	11.65%	12.98%	13.16%	25.22%	-28.31%	12.29%	39.82%	2.33%
FMDGX Fidelity Mid Cap Growth Index Fund	4.88%	8.60%	22.03%	25.79%	-26.67%	12.67%	34.84%	4.63%

Correlation

The correlation between STMGX and FMDGX is 0.94, indicating a strong positive relationship between their price movements. Combining them offers limited diversification - they tend to fall together during downturns.

	Correlation
Correlation (1Y) Calculated over the trailing 1-year period	0.94
Correlation (3Y) Calculated over the trailing 3-year period	0.94
Correlation (5Y) Calculated over the trailing 5-year period	0.96
Correlation (All Time) Calculated using the full available price history since Jul 18, 2019	0.97

The correlation between STMGX and FMDGX has been stable across timeframes, ranging from 0.94 to 0.96 - a consistent structural relationship.

Return for Risk

STMGX vs. FMDGX — Risk / Return Rank

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

STMGX

STMGX Risk / Return Rank: 26
STMGX Sharpe Ratio Rank: 24
STMGX Sortino Ratio Rank: 23
STMGX Omega Ratio Rank: 21
STMGX Calmar Ratio Rank: 32
STMGX Martin Ratio Rank: 33

FMDGX

FMDGX Risk / Return Rank: 6
FMDGX Sharpe Ratio Rank: 6
FMDGX Sortino Ratio Rank: 6
FMDGX Omega Ratio Rank: 6
FMDGX Calmar Ratio Rank: 6
FMDGX Martin Ratio Rank: 6

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.

STMGX vs. FMDGX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for American Beacon Stephens Mid-Cap Growth Fund (STMGX) and Fidelity Mid Cap Growth Index Fund (FMDGX). 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.

	STMGX	FMDGX	Difference
Sharpe ratio Return per unit of total volatility	1.41	0.49	+0.92
Sortino ratio Return per unit of downside risk	2.02	0.80	+1.22
Omega ratio Gain probability vs. loss probability	1.24	1.09	+0.15
Calmar ratio Return relative to maximum drawdown	2.11	0.54	+1.57
Martin ratio Return relative to average drawdown	7.45	1.58	+5.87
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

STMGX vs. FMDGX - Sharpe Ratio Comparison

The current STMGX Sharpe Ratio is 1.41, which is higher than the FMDGX Sharpe Ratio of 0.49. The chart below compares the historical Sharpe Ratios of STMGX and FMDGX, 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

	STMGX	FMDGX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	1.41	0.49	+0.92
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.35	0.32	+0.03
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	0.67	—	—
Sharpe Ratio (All Time) Calculated using the full available price history	0.46	0.45	+0.01

Drawdowns

STMGX vs. FMDGX - Drawdown Comparison

The maximum STMGX drawdown since its inception was -57.58%, which is greater than FMDGX's maximum drawdown of -38.59%. Use the drawdown chart below to compare losses from any high point for STMGX and FMDGX.

Drawdown Indicators

	STMGX	FMDGX	Difference
Max Drawdown Largest peak-to-trough decline	-57.58%	-38.59%	-18.99%
Max Drawdown (1Y) Largest decline over 1 year	-10.84%	-14.75%	+3.91%
Max Drawdown (3Y) Largest decline over 3 years	-22.50%	-25.30%	+2.80%
Max Drawdown (5Y) Largest decline over 5 years	-36.59%	-38.59%	+2.00%
Max Drawdown (10Y) Largest decline over 10 years	-36.59%	—	—
Current Drawdown Current decline from peak	0.00%	-1.09%	+1.09%
Average Drawdown Average peak-to-trough decline	-10.16%	-11.21%	+1.05%
Ulcer Index Depth and duration of drawdowns from previous peaks	3.07%	5.05%	-1.98%

Volatility

STMGX vs. FMDGX - Volatility Comparison

American Beacon Stephens Mid-Cap Growth Fund (STMGX) has a higher volatility of 4.24% compared to Fidelity Mid Cap Growth Index Fund (FMDGX) at 3.52%. This indicates that STMGX's price experiences larger fluctuations and is considered to be riskier than FMDGX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	STMGX	FMDGX	Difference
Volatility (1M) Calculated over the trailing 1-month period	4.24%	3.52%	+0.72%
Volatility (6M) Calculated over the trailing 6-month period	12.70%	12.64%	+0.06%
Volatility (1Y) Calculated over the trailing 1-year period	16.27%	16.46%	-0.19%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	20.83%	22.37%	-1.54%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	20.89%	24.32%	-3.43%

STMGX vs. FMDGX - Expense Ratio Comparison

STMGX has a 1.14% expense ratio, which is higher than FMDGX's 0.05% expense ratio.

Dividends

STMGX vs. FMDGX - Dividend Comparison

STMGX's dividend yield for the trailing twelve months is around 30.79%, more than FMDGX's 1.77% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
FMDGX Fidelity Mid Cap Growth Index Fund	1.77%	1.85%	0.47%	0.63%	0.81%	6.43%	0.36%	0.29%	0.00%	0.00%	0.00%	0.00%
STMGX American Beacon Stephens Mid-Cap Growth Fund	30.79%	34.38%	4.86%	0.00%	3.42%	7.49%	1.45%	3.60%	9.39%	5.40%	6.65%	5.62%

Frequently Asked Questions

Can I hold both STMGX and FMDGX in my portfolio?

With a correlation of 0.94, STMGX and FMDGX move almost identically. Holding both adds very little diversification - you're essentially doubling your position in the same market segment. Choosing one is usually more capital-efficient.

Which is riskier, STMGX or FMDGX?

STMGX has higher volatility (4.24%) compared to FMDGX (3.52%). In terms of maximum drawdown, STMGX dropped -57.58% vs FMDGX's -38.59%.

Which has better risk-adjusted returns?

STMGX currently has the higher Sharpe Ratio (1.41 vs 0.49), 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.