VMBSX vs. FNSOX

Last updated Aug 4, 2026

VMBSX (Vanguard Mortgage-Backed Securities Index Fund Admiral Shares) and FNSOX (Fidelity Short-Term Bond Index Fund) are both Total Bond Market funds. Over the past 5 years, VMBSX returned 0.27%/yr vs 1.50%/yr for FNSOX. Their 0.76 correlation means they have sometimes moved together and sometimes differently. VMBSX charges 0.07%/yr vs 0.03%/yr for FNSOX.

Performance

VMBSX vs. FNSOX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in Vanguard Mortgage-Backed Securities Index Fund Admiral Shares (VMBSX) and Fidelity Short-Term Bond Index Fund (FNSOX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, VMBSX achieves a -0.08% return, which is significantly lower than FNSOX's 0.13% return.

VMBSX

• 1D: -0.38%
• 1M: -1.02%
• 6M: -0.42%
• YTD: -0.08%
• 1Y: 3.41%
• 3Y*: 4.65%
• 5Y*: 0.27%
• 10Y*: 1.72%
• ALL TIME*: 2.31%

FNSOX

• 1D: -0.10%
• 1M: -0.40%
• 6M: -0.02%
• YTD: 0.13%
• 1Y: 2.05%
• 3Y*: 4.44%
• 5Y*: 1.50%
• 10Y*: —
• ALL TIME*: 2.00%

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

Liquidity Comparison

Position	Avg. Volume Value (2W)	Avg. Volume Value (1M)	Avg. Volume Value (3M)
FNSOX Fidelity Short-Term Bond Index Fund	$0.00	$0.00	$0.00
VMBSX Vanguard Mortgage-Backed Securities Index Fund Admiral Shares	$0.00	$0.00	$0.00

VMBSX vs. FNSOX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
VMBSX Vanguard Mortgage-Backed Securities Index Fund Admiral Shares	-0.08%	8.43%	1.76%	4.99%	-11.56%	-1.35%	3.74%	11.47%	0.87%	0.06%
FNSOX Fidelity Short-Term Bond Index Fund	0.13%	6.01%	3.90%	4.90%	-5.76%	-1.25%	4.28%	4.95%	1.14%	-0.22%

Correlation

The correlation between VMBSX and FNSOX is 0.78, which is moderate. They have sometimes moved together and sometimes differently, sharing some price drivers without tracking each other closely.

	Correlation
Correlation (1Y) Focuses on recent behavior, but can change the most.	0.78
Correlation (3Y) Balances recent behavior with more history.	0.80
Correlation (5Y) Shows whether the relationship held over a longer period.	0.83
Correlation (All Time) Calculated using the full available price history since Oct 31, 2017	0.76

The correlation between VMBSX and FNSOX has been stable across timeframes, ranging from 0.76 to 0.83 - a consistent structural relationship.

Return for Risk

VMBSX vs. FNSOX — Risk / Return Rank

Compare historical risk-adjusted metric ranks over the past 12 months.

VMBSX

VMBSX Risk / Return Rank: 32
VMBSX Sharpe Ratio Rank: 32
VMBSX Sortino Ratio Rank: 31
VMBSX Omega Ratio Rank: 31
VMBSX Calmar Ratio Rank: 34
VMBSX Martin Ratio Rank: 29

FNSOX

FNSOX Risk / Return Rank: 42
FNSOX Sharpe Ratio Rank: 41
FNSOX Sortino Ratio Rank: 48
FNSOX Omega Ratio Rank: 45
FNSOX Calmar Ratio Rank: 42
FNSOX Martin Ratio Rank: 33

The rank (0–100) uses a weighted average of the Sharpe, Sortino, Omega, Calmar, and Martin percentile ranks for the trailing 12 months. Higher means stronger historical risk-adjusted performance within the peer group.

VMBSX vs. FNSOX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for Vanguard Mortgage-Backed Securities Index Fund Admiral Shares (VMBSX) and Fidelity Short-Term Bond Index Fund (FNSOX). 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.

	VMBSX	FNSOX	Difference
Sharpe ratio: Return per unit of total volatility	1.12	1.30	-0.17
Sortino ratio: Return per unit of downside risk	1.63	2.05	-0.42
Omega ratio: Gain probability vs. loss probability	1.20	1.25	-0.05
Calmar ratio: Return relative to maximum drawdown	1.60	1.81	-0.20
Martin ratio: Return relative to average drawdown	4.52	5.15	-0.63

VMBSX vs. FNSOX - Sharpe Ratio Comparison

The current VMBSX Sharpe Ratio is 1.12, which is comparable to the FNSOX Sharpe Ratio of 1.30. The chart below compares the historical Sharpe Ratios of VMBSX and FNSOX, 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

VMBSX vs. FNSOX - Drawdown Comparison

The maximum VMBSX drawdown since its inception was -17.44%, which is greater than FNSOX's maximum drawdown of -8.92%. Use the drawdown chart below to compare losses from any high point for VMBSX and FNSOX.

Drawdown Indicators

	VMBSX	FNSOX	Difference
Max Drawdown Largest peak-to-trough decline	-17.44%	-8.92%	-8.52%
Max Drawdown (1Y) Largest decline over 1 year	-2.67%	-1.47%	-1.20%
Max Drawdown (3Y) Largest decline over 3 years	-6.43%	-1.51%	-4.92%
Max Drawdown (5Y) Largest decline over 5 years	-17.01%	-8.68%	-8.33%
Max Drawdown (10Y) Largest decline over 10 years	-17.44%	—	—
Current Drawdown Current decline from peak	-2.09%	-0.83%	-1.26%
Average Drawdown Average peak-to-trough decline	-2.47%	-1.71%	-0.76%
Ulcer Index Depth and duration of drawdowns from previous peaks	0.94%	0.52%	+0.42%

Volatility

VMBSX vs. FNSOX - Volatility Comparison

Vanguard Mortgage-Backed Securities Index Fund Admiral Shares (VMBSX) has a higher volatility of 1.17% compared to Fidelity Short-Term Bond Index Fund (FNSOX) at 0.44%. This indicates that VMBSX's price experiences larger fluctuations and is considered to be riskier than FNSOX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	VMBSX	FNSOX	Difference
Volatility (1M) Calculated over the trailing 1-month period	1.17%	0.44%	+0.73%
Volatility (6M) Calculated over the trailing 6-month period	3.05%	1.61%	+1.44%
Volatility (1Y) Calculated over the trailing 1-year period	3.81%	2.07%	+1.74%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	6.44%	2.90%	+3.54%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	4.88%	2.47%	+2.41%

VMBSX vs. FNSOX - Expense Ratio Comparison

VMBSX has a 0.07% expense ratio, which is higher than FNSOX's 0.03% expense ratio. However, both funds are considered low-cost compared to the broader market, where average expense ratios usually range from 0.3% to 0.9%.

Dividends

VMBSX vs. FNSOX - Dividend Comparison

VMBSX's dividend yield for the trailing twelve months is around 3.87%, more than FNSOX's 3.36% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
FNSOX Fidelity Short-Term Bond Index Fund	3.36%	3.22%	2.80%	1.74%	0.81%	0.80%	1.54%	2.61%	2.04%	0.34%	0.00%	0.00%
VMBSX Vanguard Mortgage-Backed Securities Index Fund Admiral Shares	3.87%	4.18%	4.24%	3.28%	2.31%	0.99%	2.00%	7.48%	2.72%	2.16%	1.98%	2.01%

Frequently Asked Questions

Can I hold both VMBSX and FNSOX in my portfolio?

VMBSX and FNSOX have a correlation of 0.78, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, VMBSX or FNSOX?

VMBSX has higher volatility (1.17%) compared to FNSOX (0.44%). In terms of maximum drawdown, VMBSX dropped -17.44% vs FNSOX's -8.92%.

Which has better risk-adjusted returns?

FNSOX currently has the higher Sharpe Ratio (1.30 vs 1.12), 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.