AULDX vs. FXAIX

Last updated Jun 4, 2026

AULDX (American Century Ultra Fund Class R6) and FXAIX (Fidelity 500 Index Fund) are both mutual funds - AULDX is a Large Cap Growth Equities fund actively managed by American Century, while FXAIX is a S&P 500 fund tracking the S&P 500 Index. AULDX is actively managed, while FXAIX is passively managed. Over the past 10 years, AULDX returned 18.69%/yr vs 15.66%/yr for FXAIX. Their correlation of 0.92 suggests significant overlap in exposure. AULDX charges 0.52%/yr vs 0.02%/yr for FXAIX.

Performance

AULDX vs. FXAIX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in American Century Ultra Fund Class R6 (AULDX) and Fidelity 500 Index Fund (FXAIX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, AULDX achieves a 9.84% return, which is significantly lower than FXAIX's 11.71% return. Over the past 10 years, AULDX has outperformed FXAIX with an annualized return of 18.69%, while FXAIX has yielded a comparatively lower 15.66% annualized return.

AULDX

• 1D: -0.38%
• 1M: 6.26%
• YTD: 9.84%
• 6M: 8.20%
• 1Y: 26.07%
• 3Y*: 22.37%
• 5Y*: 13.43%
• 10Y*: 18.69%

FXAIX

• 1D: 0.13%
• 1M: 5.80%
• YTD: 11.71%
• 6M: 11.74%
• 1Y: 28.99%
• 3Y*: 22.75%
• 5Y*: 14.28%
• 10Y*: 15.66%

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

AULDX vs. FXAIX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
AULDX American Century Ultra Fund Class R6	9.84%	13.05%	29.99%	43.86%	-32.15%	23.89%	50.31%	35.23%	1.04%	32.36%
FXAIX Fidelity 500 Index Fund	11.71%	17.84%	25.01%	26.29%	-18.14%	28.71%	18.42%	31.48%	-4.43%	21.82%

Correlation

The correlation between AULDX and FXAIX is 0.91, 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	0.91
Correlation (3Y) Calculated over the trailing 3-year period	0.92
Correlation (5Y) Calculated over the trailing 5-year period	0.93
Correlation (10Y) Calculated over the trailing 10-year period	0.92
Correlation (All Time) Calculated using the full available price history since Jan 3, 2014	0.92

The correlation between AULDX and FXAIX has been stable across timeframes, ranging from 0.91 to 0.93 - a consistent structural relationship.

Return for Risk

AULDX vs. FXAIX — Risk / Return Rank

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

AULDX

AULDX Risk / Return Rank: 28
AULDX Sharpe Ratio Rank: 33
AULDX Sortino Ratio Rank: 29
AULDX Omega Ratio Rank: 30
AULDX Calmar Ratio Rank: 22
AULDX Martin Ratio Rank: 25

FXAIX

FXAIX Risk / Return Rank: 73
FXAIX Sharpe Ratio Rank: 76
FXAIX Sortino Ratio Rank: 67
FXAIX Omega Ratio Rank: 67
FXAIX Calmar Ratio Rank: 74
FXAIX Martin Ratio Rank: 83

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.

AULDX vs. FXAIX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for American Century Ultra Fund Class R6 (AULDX) and Fidelity 500 Index Fund (FXAIX). 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.

	AULDX	FXAIX	Difference
Sharpe ratio: Return per unit of total volatility	1.65	2.52	-0.87
Sortino ratio: Return per unit of downside risk	2.26	3.42	-1.16
Omega ratio: Gain probability vs. loss probability	1.29	1.46	-0.17
Calmar ratio: Return relative to maximum drawdown	1.72	3.36	-1.64
Martin ratio: Return relative to average drawdown	6.07	15.70	-9.62
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

AULDX vs. FXAIX - Sharpe Ratio Comparison

The current AULDX Sharpe Ratio is 1.65, which is lower than the FXAIX Sharpe Ratio of 2.52. The chart below compares the historical Sharpe Ratios of AULDX and FXAIX, 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

	AULDX	FXAIX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	1.65	2.52	-0.87
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.60	0.85	-0.25
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	0.85	0.87	-0.02
Sharpe Ratio (All Time) Calculated using the full available price history	0.78	0.82	-0.04

Drawdowns

AULDX vs. FXAIX - Drawdown Comparison

The maximum AULDX drawdown since its inception was -35.03%, roughly equal to the maximum FXAIX drawdown of -33.79%. Use the drawdown chart below to compare losses from any high point for AULDX and FXAIX.

Drawdown Indicators

	AULDX	FXAIX	Difference
Max Drawdown Largest peak-to-trough decline	-35.03%	-33.79%	-1.24%
Max Drawdown (1Y) Largest decline over 1 year	-15.60%	-8.89%	-6.71%
Max Drawdown (3Y) Largest decline over 3 years	-24.78%	-18.76%	-6.02%
Max Drawdown (5Y) Largest decline over 5 years	-35.03%	-24.50%	-10.53%
Max Drawdown (10Y) Largest decline over 10 years	-35.03%	-33.79%	-1.24%
Current Drawdown Current decline from peak	-0.38%	0.00%	-0.38%
Average Drawdown Average peak-to-trough decline	-6.19%	-3.79%	-2.40%
Ulcer Index Depth and duration of drawdowns from previous peaks	4.42%	1.90%	+2.52%

Volatility

AULDX vs. FXAIX - Volatility Comparison

American Century Ultra Fund Class R6 (AULDX) has a higher volatility of 3.77% compared to Fidelity 500 Index Fund (FXAIX) at 2.83%. This indicates that AULDX's price experiences larger fluctuations and is considered to be riskier than FXAIX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	AULDX	FXAIX	Difference
Volatility (1M) Calculated over the trailing 1-month period	3.77%	2.83%	+0.94%
Volatility (6M) Calculated over the trailing 6-month period	12.32%	8.97%	+3.35%
Volatility (1Y) Calculated over the trailing 1-year period	16.30%	11.86%	+4.44%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	22.57%	16.91%	+5.66%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	22.08%	18.07%	+4.01%

AULDX vs. FXAIX - Expense Ratio Comparison

AULDX has a 0.52% expense ratio, which is higher than FXAIX's 0.02% expense ratio.

Dividends

AULDX vs. FXAIX - Dividend Comparison

AULDX's dividend yield for the trailing twelve months is around 9.65%, more than FXAIX's 1.03% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
AULDX American Century Ultra Fund Class R6	9.65%	10.60%	3.32%	5.68%	6.97%	6.42%	2.67%	4.18%	7.94%	6.19%	4.45%	5.06%
FXAIX Fidelity 500 Index Fund	1.03%	1.11%	1.25%	1.45%	1.69%	1.22%	1.60%	2.06%	2.72%	1.97%	2.52%	2.83%

Frequently Asked Questions

Can I hold both AULDX and FXAIX in my portfolio?

With a correlation of 0.91, AULDX and FXAIX 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, AULDX or FXAIX?

AULDX has higher volatility (3.77%) compared to FXAIX (2.83%). In terms of maximum drawdown, AULDX dropped -35.03% vs FXAIX's -33.79%.

Which has better risk-adjusted returns?

FXAIX currently has the higher Sharpe Ratio (2.52 vs 1.65), 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.