FLXSX vs. FDFIX

Last updated Jun 4, 2026

FLXSX (Fidelity Flex Small Cap Index Fund) and FDFIX (Fidelity Flex 500 Index Fund) are both mutual funds - FLXSX is a Small Cap Blend Equities fund managed by Fidelity, while FDFIX is a Large Cap Blend Equities fund managed by Fidelity. Over the past 5 years, FLXSX returned 6.27%/yr vs 14.20%/yr for FDFIX. Their correlation of 0.81 suggests significant overlap in exposure. Both charge a 0.00% expense ratio.

Performance

FLXSX vs. FDFIX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in Fidelity Flex Small Cap Index Fund (FLXSX) and Fidelity Flex 500 Index Fund (FDFIX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, FLXSX achieves a 17.21% return, which is significantly higher than FDFIX's 11.53% return.

FLXSX

• 1D: 0.33%
• 1M: 3.96%
• YTD: 17.21%
• 6M: 16.56%
• 1Y: 38.39%
• 3Y*: 17.93%
• 5Y*: 6.27%
• 10Y*: —

FDFIX

• 1D: 0.22%
• 1M: 6.02%
• YTD: 11.53%
• 6M: 11.45%
• 1Y: 28.49%
• 3Y*: 22.62%
• 5Y*: 14.20%
• 10Y*: —

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

FLXSX vs. FDFIX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
FLXSX Fidelity Flex Small Cap Index Fund	17.21%	12.02%	11.67%	17.11%	-20.29%	14.84%	20.06%	25.69%	-11.13%	14.28%
FDFIX Fidelity Flex 500 Index Fund	11.53%	17.59%	25.06%	26.27%	-18.10%	28.69%	18.46%	31.47%	-4.45%	14.41%

Correlation

The correlation between FLXSX and FDFIX is 0.79, 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	0.79
Correlation (3Y) Calculated over the trailing 3-year period	0.77
Correlation (5Y) Calculated over the trailing 5-year period	0.82
Correlation (All Time) Calculated using the full available price history since Mar 10, 2017	0.81

The correlation between FLXSX and FDFIX has been stable across timeframes, ranging from 0.77 to 0.82 - a consistent structural relationship.

Return for Risk

FLXSX vs. FDFIX — Risk / Return Rank

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

FLXSX

FLXSX Risk / Return Rank: 54
FLXSX Sharpe Ratio Rank: 49
FLXSX Sortino Ratio Rank: 46
FLXSX Omega Ratio Rank: 40
FLXSX Calmar Ratio Rank: 73
FLXSX Martin Ratio Rank: 59

FDFIX

FDFIX Risk / Return Rank: 70
FDFIX Sharpe Ratio Rank: 72
FDFIX Sortino Ratio Rank: 64
FDFIX Omega Ratio Rank: 64
FDFIX Calmar Ratio Rank: 72
FDFIX Martin Ratio Rank: 80

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.

FLXSX vs. FDFIX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for Fidelity Flex Small Cap Index Fund (FLXSX) and Fidelity Flex 500 Index Fund (FDFIX). 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.

	FLXSX	FDFIX	Difference
Sharpe ratio: Return per unit of total volatility	2.08	2.47	-0.39
Sortino ratio: Return per unit of downside risk	2.86	3.34	-0.49
Omega ratio: Gain probability vs. loss probability	1.34	1.45	-0.11
Calmar ratio: Return relative to maximum drawdown	3.35	3.28	+0.06
Martin ratio: Return relative to average drawdown	11.73	14.96	-3.23
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

FLXSX vs. FDFIX - Sharpe Ratio Comparison

The current FLXSX Sharpe Ratio is 2.08, which is comparable to the FDFIX Sharpe Ratio of 2.47. The chart below compares the historical Sharpe Ratios of FLXSX and FDFIX, 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

	FLXSX	FDFIX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	2.08	2.47	-0.39
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.28	0.84	-0.56
Sharpe Ratio (All Time) Calculated using the full available price history	0.42	0.82	-0.41

Drawdowns

FLXSX vs. FDFIX - Drawdown Comparison

The maximum FLXSX drawdown since its inception was -41.72%, which is greater than FDFIX's maximum drawdown of -33.77%. Use the drawdown chart below to compare losses from any high point for FLXSX and FDFIX.

Drawdown Indicators

	FLXSX	FDFIX	Difference
Max Drawdown Largest peak-to-trough decline	-41.72%	-33.77%	-7.95%
Max Drawdown (1Y) Largest decline over 1 year	-12.25%	-8.99%	-3.26%
Max Drawdown (3Y) Largest decline over 3 years	-27.48%	-18.76%	-8.72%
Max Drawdown (5Y) Largest decline over 5 years	-31.88%	-24.51%	-7.37%
Current Drawdown Current decline from peak	-0.19%	0.00%	-0.19%
Average Drawdown Average peak-to-trough decline	-10.44%	-4.58%	-5.86%
Ulcer Index Depth and duration of drawdowns from previous peaks	3.48%	1.97%	+1.51%

Volatility

FLXSX vs. FDFIX - Volatility Comparison

Fidelity Flex Small Cap Index Fund (FLXSX) has a higher volatility of 5.03% compared to Fidelity Flex 500 Index Fund (FDFIX) at 2.92%. This indicates that FLXSX's price experiences larger fluctuations and is considered to be riskier than FDFIX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	FLXSX	FDFIX	Difference
Volatility (1M) Calculated over the trailing 1-month period	5.03%	2.92%	+2.11%
Volatility (6M) Calculated over the trailing 6-month period	14.19%	9.03%	+5.16%
Volatility (1Y) Calculated over the trailing 1-year period	19.72%	11.96%	+7.76%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	22.66%	16.95%	+5.71%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	24.00%	18.59%	+5.41%

FLXSX vs. FDFIX - Expense Ratio Comparison

FLXSX has a 0.00% expense ratio, which is lower than FDFIX's 0.00% expense ratio. Despite the difference, both funds are considered low-cost compared to the broader market, where average expense ratios usually range from 0.3% to 0.9%.

Dividends

FLXSX vs. FDFIX - Dividend Comparison

FLXSX has not paid dividends to shareholders, while FDFIX's dividend yield for the trailing twelve months is around 1.03%.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017
FDFIX Fidelity Flex 500 Index Fund	1.03%	1.11%	1.26%	1.48%	1.70%	1.27%	1.52%	1.78%	2.16%	0.50%
FLXSX Fidelity Flex Small Cap Index Fund	0.00%	0.00%	1.36%	1.49%	1.26%	2.74%	1.06%	2.86%	2.31%	0.77%

Frequently Asked Questions

Can I hold both FLXSX and FDFIX in my portfolio?

FLXSX and FDFIX have a correlation of 0.79, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, FLXSX or FDFIX?

FLXSX has higher volatility (5.03%) compared to FDFIX (2.92%). In terms of maximum drawdown, FLXSX dropped -41.72% vs FDFIX's -33.77%.

Which has better risk-adjusted returns?

FDFIX currently has the higher Sharpe Ratio (2.47 vs 2.08), 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.