FSMTX vs. VMBSX

Last updated Jun 4, 2026

FSMTX (Fidelity SAI Total Bond Fund) and VMBSX (Vanguard Mortgage-Backed Securities Index Fund Admiral Shares) are both Total Bond Market funds. Over the past 5 years, FSMTX returned 1.02%/yr vs 0.55%/yr for VMBSX. Their correlation of 0.84 suggests significant overlap in exposure. FSMTX charges 0.30%/yr vs 0.07%/yr for VMBSX.

Performance

FSMTX vs. VMBSX - Performance Comparison

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

Returns By Period

In the year-to-date period, FSMTX achieves a 0.57% return, which is significantly lower than VMBSX's 0.81% return.

FSMTX

• 1D: 0.00%
• 1M: 0.48%
• YTD: 0.57%
• 6M: 0.55%
• 1Y: 5.80%
• 3Y*: 5.18%
• 5Y*: 1.02%
• 10Y*: —

VMBSX

• 1D: 0.00%
• 1M: 0.46%
• YTD: 0.81%
• 6M: 0.99%
• 1Y: 6.98%
• 3Y*: 4.69%
• 5Y*: 0.55%
• 10Y*: 1.87%

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

FSMTX vs. VMBSX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018
FSMTX Fidelity SAI Total Bond Fund	0.57%	7.65%	2.93%	7.33%	-13.30%	-0.30%	8.13%	9.87%	1.41%
VMBSX Vanguard Mortgage-Backed Securities Index Fund Admiral Shares	0.81%	8.43%	1.76%	4.99%	-11.56%	-1.35%	3.74%	11.47%	2.61%

Correlation

The correlation between FSMTX and VMBSX is 0.90, 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	0.90
Correlation (3Y) Calculated over the trailing 3-year period	0.91
Correlation (5Y) Calculated over the trailing 5-year period	0.90
Correlation (All Time) Calculated using the full available price history since Nov 1, 2018	0.84

The correlation between FSMTX and VMBSX has been stable across timeframes, ranging from 0.84 to 0.91 - a consistent structural relationship.

Return for Risk

FSMTX vs. VMBSX — Risk / Return Rank

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

FSMTX

FSMTX Risk / Return Rank: 28
FSMTX Sharpe Ratio Rank: 28
FSMTX Sortino Ratio Rank: 30
FSMTX Omega Ratio Rank: 27
FSMTX Calmar Ratio Rank: 31
FSMTX Martin Ratio Rank: 25

VMBSX

VMBSX Risk / Return Rank: 42
VMBSX Sharpe Ratio Rank: 40
VMBSX Sortino Ratio Rank: 42
VMBSX Omega Ratio Rank: 40
VMBSX Calmar Ratio Rank: 48
VMBSX Martin Ratio Rank: 41

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.

FSMTX vs. VMBSX - Risk-Adjusted Trends Comparison

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

	FSMTX	VMBSX	Difference
Sharpe ratio Return per unit of total volatility	1.52	1.84	-0.32
Sortino ratio Return per unit of downside risk	2.29	2.75	-0.46
Omega ratio Gain probability vs. loss probability	1.27	1.34	-0.07
Calmar ratio Return relative to maximum drawdown	2.09	2.63	-0.54
Martin ratio Return relative to average drawdown	6.19	8.86	-2.67
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

FSMTX vs. VMBSX - Sharpe Ratio Comparison

The current FSMTX Sharpe Ratio is 1.52, which is comparable to the VMBSX Sharpe Ratio of 1.84. The chart below compares the historical Sharpe Ratios of FSMTX and VMBSX, 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

	FSMTX	VMBSX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	1.52	1.84	-0.32
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.18	0.09	+0.09
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	—	0.39	—
Sharpe Ratio (All Time) Calculated using the full available price history	0.57	0.59	-0.02

Drawdowns

FSMTX vs. VMBSX - Drawdown Comparison

The maximum FSMTX drawdown since its inception was -17.89%, roughly equal to the maximum VMBSX drawdown of -17.44%. Use the drawdown chart below to compare losses from any high point for FSMTX and VMBSX.

Drawdown Indicators

	FSMTX	VMBSX	Difference
Max Drawdown Largest peak-to-trough decline	-17.89%	-17.44%	-0.45%
Max Drawdown (1Y) Largest decline over 1 year	-2.86%	-2.67%	-0.19%
Max Drawdown (3Y) Largest decline over 3 years	-5.85%	-7.53%	+1.68%
Max Drawdown (5Y) Largest decline over 5 years	-17.89%	-17.12%	-0.77%
Max Drawdown (10Y) Largest decline over 10 years	—	-17.44%	—
Current Drawdown Current decline from peak	-1.29%	-1.22%	-0.07%
Average Drawdown Average peak-to-trough decline	-4.47%	-2.48%	-1.99%
Ulcer Index Depth and duration of drawdowns from previous peaks	0.96%	0.79%	+0.17%

Volatility

FSMTX vs. VMBSX - Volatility Comparison

The current volatility for Fidelity SAI Total Bond Fund (FSMTX) is 1.36%, while Vanguard Mortgage-Backed Securities Index Fund Admiral Shares (VMBSX) has a volatility of 1.46%. This indicates that FSMTX experiences smaller price fluctuations and is considered to be less risky than VMBSX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	FSMTX	VMBSX	Difference
Volatility (1M) Calculated over the trailing 1-month period	1.36%	1.46%	-0.10%
Volatility (6M) Calculated over the trailing 6-month period	2.76%	2.73%	+0.03%
Volatility (1Y) Calculated over the trailing 1-year period	3.93%	3.82%	+0.11%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	5.70%	6.40%	-0.70%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	5.22%	4.86%	+0.36%

FSMTX vs. VMBSX - Expense Ratio Comparison

FSMTX has a 0.30% expense ratio, which is higher than VMBSX's 0.07% expense ratio.

Dividends

FSMTX vs. VMBSX - Dividend Comparison

FSMTX's dividend yield for the trailing twelve months is around 4.56%, more than VMBSX's 4.16% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
FSMTX Fidelity SAI Total Bond Fund	4.56%	4.56%	4.70%	4.29%	2.59%	2.74%	5.36%	4.93%	0.62%	0.00%	0.00%	0.00%
VMBSX Vanguard Mortgage-Backed Securities Index Fund Admiral Shares	4.16%	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 FSMTX and VMBSX in my portfolio?

With a correlation of 0.90, FSMTX and VMBSX 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, FSMTX or VMBSX?

VMBSX has higher volatility (1.46%) compared to FSMTX (1.36%). In terms of maximum drawdown, FSMTX dropped -17.89% vs VMBSX's -17.44%.

Which has better risk-adjusted returns?

VMBSX currently has the higher Sharpe Ratio (1.84 vs 1.52), 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.