VTSPX vs. APOIX

Last updated Jun 25, 2026

VTSPX (Vanguard Short-Term Inflation-Protected Securities Index Fund Institutional Shares) and APOIX (American Century Short Duration Inflation Protection Bond Fund Investor Class) are both Inflation-Protected Bonds funds. Over the past 10 years, VTSPX returned 3.05%/yr vs 3.01%/yr for APOIX. Their correlation of 0.88 suggests significant overlap in exposure. VTSPX charges 0.04%/yr vs 0.57%/yr for APOIX.

Performance

VTSPX vs. APOIX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in Vanguard Short-Term Inflation-Protected Securities Index Fund Institutional Shares (VTSPX) and American Century Short Duration Inflation Protection Bond Fund Investor Class (APOIX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, VTSPX achieves a 1.34% return, which is significantly higher than APOIX's 1.19% return. Both investments have delivered pretty close results over the past 10 years, with VTSPX having a 3.05% annualized return and APOIX not far behind at 3.01%.

VTSPX

• 1D: 0.00%
• 1M: -0.16%
• YTD: 1.34%
• 6M: 1.42%
• 1Y: 3.60%
• 3Y*: 5.01%
• 5Y*: 3.28%
• 10Y*: 3.05%

APOIX

• 1D: 0.00%
• 1M: -0.35%
• YTD: 1.19%
• 6M: 1.19%
• 1Y: 3.18%
• 3Y*: 4.62%
• 5Y*: 2.84%
• 10Y*: 3.01%

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

VTSPX vs. APOIX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
VTSPX Vanguard Short-Term Inflation-Protected Securities Index Fund Institutional Shares	1.34%	6.06%	4.75%	4.61%	-2.82%	5.32%	4.99%	4.82%	0.59%	0.83%
APOIX American Century Short Duration Inflation Protection Bond Fund Investor Class	1.19%	5.95%	4.15%	3.82%	-3.89%	6.30%	5.06%	4.77%	1.81%	0.73%

Correlation

The correlation between VTSPX and APOIX is 0.86, 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	0.86
Correlation (3Y) Calculated over the trailing 3-year period	0.91
Correlation (5Y) Calculated over the trailing 5-year period	0.92
Correlation (10Y) Calculated over the trailing 10-year period	0.88
Correlation (All Time) Calculated using the full available price history since Jan 2, 2013	0.88

The correlation between VTSPX and APOIX has been stable across timeframes, ranging from 0.86 to 0.92 - a consistent structural relationship.

Return for Risk

VTSPX vs. APOIX — Risk / Return Rank

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

VTSPX

VTSPX Risk / Return Rank: 84
VTSPX Sharpe Ratio Rank: 72
VTSPX Sortino Ratio Rank: 82
VTSPX Omega Ratio Rank: 80
VTSPX Calmar Ratio Rank: 92
VTSPX Martin Ratio Rank: 91

APOIX

APOIX Risk / Return Rank: 62
APOIX Sharpe Ratio Rank: 44
APOIX Sortino Ratio Rank: 51
APOIX Omega Ratio Rank: 52
APOIX Calmar Ratio Rank: 87
APOIX Martin Ratio Rank: 76

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.

VTSPX vs. APOIX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for Vanguard Short-Term Inflation-Protected Securities Index Fund Institutional Shares (VTSPX) and American Century Short Duration Inflation Protection Bond Fund Investor Class (APOIX). 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.

	VTSPX	APOIX	Difference
Sharpe ratio: Return per unit of total volatility	2.27	1.72	+0.55
Sortino ratio: Return per unit of downside risk	3.56	2.64	+0.92
Omega ratio: Gain probability vs. loss probability	1.47	1.35	+0.13
Calmar ratio: Return relative to maximum drawdown	4.77	3.86	+0.91
Martin ratio: Return relative to average drawdown	17.35	12.72	+4.63

VTSPX vs. APOIX - Sharpe Ratio Comparison

The current VTSPX Sharpe Ratio is 2.27, which is higher than the APOIX Sharpe Ratio of 1.72. The chart below compares the historical Sharpe Ratios of VTSPX and APOIX, 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

VTSPX vs. APOIX - Drawdown Comparison

The maximum VTSPX drawdown since its inception was -5.35%, smaller than the maximum APOIX drawdown of -14.54%. Use the drawdown chart below to compare losses from any high point for VTSPX and APOIX.

Drawdown Indicators

	VTSPX	APOIX	Difference
Max Drawdown Largest peak-to-trough decline	-5.35%	-14.54%	+9.19%
Max Drawdown (1Y) Largest decline over 1 year	-0.75%	-0.82%	+0.07%
Max Drawdown (3Y) Largest decline over 3 years	-0.92%	-1.42%	+0.50%
Max Drawdown (5Y) Largest decline over 5 years	-5.35%	-6.58%	+1.23%
Max Drawdown (10Y) Largest decline over 10 years	-5.35%	-6.58%	+1.23%
Current Drawdown Current decline from peak	-0.75%	-0.82%	+0.07%
Average Drawdown Average peak-to-trough decline	-1.01%	-1.99%	+0.98%
Ulcer Index Depth and duration of drawdowns from previous peaks	0.21%	0.25%	-0.04%

Volatility

VTSPX vs. APOIX - Volatility Comparison

Vanguard Short-Term Inflation-Protected Securities Index Fund Institutional Shares (VTSPX) and American Century Short Duration Inflation Protection Bond Fund Investor Class (APOIX) have volatilities of 0.67% and 0.66%, respectively, indicating that both stocks experience similar levels of price fluctuations. This suggests that the risk associated with both stocks, as measured by volatility, is nearly the same. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	VTSPX	APOIX	Difference
Volatility (1M) Calculated over the trailing 1-month period	0.67%	0.66%	+0.01%
Volatility (6M) Calculated over the trailing 6-month period	1.22%	1.35%	-0.13%
Volatility (1Y) Calculated over the trailing 1-year period	1.58%	1.85%	-0.27%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	2.66%	3.31%	-0.65%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	2.24%	2.85%	-0.61%

VTSPX vs. APOIX - Expense Ratio Comparison

VTSPX has a 0.04% expense ratio, which is lower than APOIX's 0.57% expense ratio.

Dividends

VTSPX vs. APOIX - Dividend Comparison

VTSPX's dividend yield for the trailing twelve months is around 3.61%, more than APOIX's 3.55% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016
APOIX American Century Short Duration Inflation Protection Bond Fund Investor Class	3.55%	3.99%	2.31%	2.78%	5.63%	3.92%	0.81%	1.69%	3.99%	1.52%	0.42%
VTSPX Vanguard Short-Term Inflation-Protected Securities Index Fund Institutional Shares	3.61%	3.81%	2.70%	2.86%	6.84%	4.69%	1.21%	1.96%	2.47%	1.52%	0.80%

Frequently Asked Questions

Can I hold both VTSPX and APOIX in my portfolio?

VTSPX and APOIX have a correlation of 0.86, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, VTSPX or APOIX?

VTSPX has higher volatility (0.67%) compared to APOIX (0.66%). In terms of maximum drawdown, VTSPX dropped -5.35% vs APOIX's -14.54%.

Which has better risk-adjusted returns?

VTSPX currently has the higher Sharpe Ratio (2.27 vs 1.72), 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.