VMBIX vs. VUBFX

Last updated Jun 3, 2026

VMBIX (Vanguard Mortgage-Backed Securities Index Fund Institutional Shares) and VUBFX (Vanguard Ultra-Short-Term Bond Fund Investor Shares) are both Total Bond Market funds from Vanguard. Over the past 10 years, VMBIX returned 1.40%/yr vs 2.61%/yr for VUBFX. At a 0.40 correlation, their price movements are largely independent. VMBIX charges 0.05%/yr vs 0.20%/yr for VUBFX.

Performance

VMBIX vs. VUBFX - Performance Comparison

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

Returns By Period

In the year-to-date period, VMBIX achieves a 0.82% return, which is significantly lower than VUBFX's 1.37% return. Over the past 10 years, VMBIX has underperformed VUBFX with an annualized return of 1.40%, while VUBFX has yielded a comparatively higher 2.61% annualized return.

VMBIX

• 1D: -0.12%
• 1M: 0.03%
• YTD: 0.82%
• 6M: 1.13%
• 1Y: 6.96%
• 3Y*: 4.70%
• 5Y*: 0.54%
• 10Y*: 1.40%

VUBFX

• 1D: 0.00%
• 1M: 0.35%
• YTD: 1.37%
• 6M: 1.75%
• 1Y: 4.40%
• 3Y*: 5.33%
• 5Y*: 3.40%
• 10Y*: 2.61%

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

VMBIX vs. VUBFX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
VMBIX Vanguard Mortgage-Backed Securities Index Fund Institutional Shares	0.82%	8.44%	1.78%	4.97%	-11.56%	-1.30%	3.77%	6.19%	0.88%	2.38%
VUBFX Vanguard Ultra-Short-Term Bond Fund Investor Shares	1.37%	5.04%	5.99%	5.43%	-0.53%	0.03%	1.95%	3.34%	1.94%	1.23%

Correlation

The correlation between VMBIX and VUBFX is 0.40, which is low. Their price movements are largely independent, making them effective diversification partners.

	Correlation
Correlation (1Y) Calculated over the trailing 1-year period	0.40
Correlation (3Y) Calculated over the trailing 3-year period	0.49
Correlation (5Y) Calculated over the trailing 5-year period	0.52
Correlation (10Y) Calculated over the trailing 10-year period	0.40
Correlation (All Time) Calculated using the full available price history since Jan 5, 2016	0.40

The correlation between VMBIX and VUBFX shifts across timeframes, from 0.40 (1 year) to 0.52 (5 years), reflecting how their relationship changes across market environments.

Return for Risk

VMBIX vs. VUBFX — Risk / Return Rank

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

VMBIX

VMBIX Risk / Return Rank: 41
VMBIX Sharpe Ratio Rank: 37
VMBIX Sortino Ratio Rank: 40
VMBIX Omega Ratio Rank: 37
VMBIX Calmar Ratio Rank: 48
VMBIX Martin Ratio Rank: 43

VUBFX

VUBFX Risk / Return Rank: 100
VUBFX Sharpe Ratio Rank: 100
VUBFX Sortino Ratio Rank: 100
VUBFX Omega Ratio Rank: 100
VUBFX Calmar Ratio Rank: 99
VUBFX Martin Ratio Rank: 100

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.

VMBIX vs. VUBFX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for Vanguard Mortgage-Backed Securities Index Fund Institutional Shares (VMBIX) and Vanguard Ultra-Short-Term Bond Fund Investor Shares (VUBFX). 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.

	VMBIX	VUBFX	Difference
Sharpe ratio Return per unit of total volatility	1.76	5.71	-3.95
Sortino ratio Return per unit of downside risk	2.64	12.83	-10.19
Omega ratio Gain probability vs. loss probability	1.32	4.52	-3.20
Calmar ratio Return relative to maximum drawdown	2.64	14.79	-12.15
Martin ratio Return relative to average drawdown	9.10	83.04	-73.95
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

VMBIX vs. VUBFX - Sharpe Ratio Comparison

The current VMBIX Sharpe Ratio is 1.76, which is lower than the VUBFX Sharpe Ratio of 5.71. The chart below compares the historical Sharpe Ratios of VMBIX and VUBFX, 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

	VMBIX	VUBFX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	1.76	5.71	-3.95
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.09	3.47	-3.39
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	0.29	3.14	-2.85
Sharpe Ratio (All Time) Calculated using the full available price history	0.51	3.11	-2.60

Drawdowns

VMBIX vs. VUBFX - Drawdown Comparison

The maximum VMBIX drawdown since its inception was -17.44%, which is greater than VUBFX's maximum drawdown of -1.86%. Use the drawdown chart below to compare losses from any high point for VMBIX and VUBFX.

Drawdown Indicators

	VMBIX	VUBFX	Difference
Max Drawdown Largest peak-to-trough decline	-17.44%	-1.86%	-15.58%
Max Drawdown (1Y) Largest decline over 1 year	-2.63%	-0.30%	-2.33%
Max Drawdown (3Y) Largest decline over 3 years	-7.51%	-0.30%	-7.21%
Max Drawdown (5Y) Largest decline over 5 years	-17.11%	-1.86%	-15.25%
Max Drawdown (10Y) Largest decline over 10 years	-17.44%	-1.86%	-15.58%
Current Drawdown Current decline from peak	-1.19%	0.00%	-1.19%
Average Drawdown Average peak-to-trough decline	-2.51%	-0.17%	-2.34%
Ulcer Index Depth and duration of drawdowns from previous peaks	0.76%	0.05%	+0.71%

Volatility

VMBIX vs. VUBFX - Volatility Comparison

Vanguard Mortgage-Backed Securities Index Fund Institutional Shares (VMBIX) has a higher volatility of 1.47% compared to Vanguard Ultra-Short-Term Bond Fund Investor Shares (VUBFX) at 0.17%. This indicates that VMBIX's price experiences larger fluctuations and is considered to be riskier than VUBFX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	VMBIX	VUBFX	Difference
Volatility (1M) Calculated over the trailing 1-month period	1.47%	0.17%	+1.30%
Volatility (6M) Calculated over the trailing 6-month period	2.77%	0.54%	+2.23%
Volatility (1Y) Calculated over the trailing 1-year period	3.81%	0.77%	+3.04%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	6.37%	0.99%	+5.38%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	4.79%	0.83%	+3.96%

VMBIX vs. VUBFX - Expense Ratio Comparison

VMBIX has a 0.05% expense ratio, which is lower than VUBFX's 0.20% 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

VMBIX vs. VUBFX - Dividend Comparison

VMBIX's dividend yield for the trailing twelve months is around 4.18%, less than VUBFX's 4.42% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
VMBIX Vanguard Mortgage-Backed Securities Index Fund Institutional Shares	4.18%	4.20%	4.27%	3.29%	2.33%	1.01%	2.02%	2.76%	2.74%	2.18%	2.13%	2.04%
VUBFX Vanguard Ultra-Short-Term Bond Fund Investor Shares	4.42%	4.62%	5.42%	4.06%	1.28%	0.43%	1.52%	2.58%	2.13%	1.43%	0.98%	0.00%

Frequently Asked Questions

Can I hold both VMBIX and VUBFX in my portfolio?

VMBIX and VUBFX have a correlation of 0.40, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, VMBIX or VUBFX?

VMBIX has higher volatility (1.47%) compared to VUBFX (0.17%). In terms of maximum drawdown, VMBIX dropped -17.44% vs VUBFX's -1.86%.

Which has better risk-adjusted returns?

VUBFX currently has the higher Sharpe Ratio (5.71 vs 1.76), 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.