VMBSX vs. VCOBX
VMBSX (Vanguard Mortgage-Backed Securities Index Fund Admiral Shares) and VCOBX (Vanguard Core Bond Fund Admiral Shares) are both Total Bond Market funds from Vanguard. Over the past 10 years, VMBSX returned 1.85%/yr vs 2.17%/yr for VCOBX. Their correlation of 0.88 suggests significant overlap in exposure. VMBSX charges 0.07%/yr vs 0.10%/yr for VCOBX.
Performance
VMBSX vs. VCOBX - Performance Comparison
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Returns By Period
In the year-to-date period, VMBSX achieves a 0.60% return, which is significantly higher than VCOBX's 0.43% return. Over the past 10 years, VMBSX has underperformed VCOBX with an annualized return of 1.85%, while VCOBX has yielded a comparatively higher 2.17% annualized return.
VMBSX
- 1D
- -0.21%
- 1M
- 0.08%
- YTD
- 0.60%
- 6M
- 0.94%
- 1Y
- 6.11%
- 3Y*
- 4.62%
- 5Y*
- 0.47%
- 10Y*
- 1.85%
VCOBX
- 1D
- -0.17%
- 1M
- 0.16%
- YTD
- 0.43%
- 6M
- 0.52%
- 1Y
- 4.91%
- 3Y*
- 4.84%
- 5Y*
- 0.55%
- 10Y*
- 2.17%
VMBSX vs. VCOBX - Yearly Performance Comparison
| 2026 (YTD) | 2025 | 2024 | 2023 | 2022 | 2021 | 2020 | 2019 | 2018 | 2017 | |
|---|---|---|---|---|---|---|---|---|---|---|
VMBSX Vanguard Mortgage-Backed Securities Index Fund Admiral Shares | 0.60% | 8.43% | 1.76% | 4.99% | -11.56% | -1.35% | 3.74% | 11.47% | 0.87% | 2.32% |
VCOBX Vanguard Core Bond Fund Admiral Shares | 0.43% | 7.73% | 2.21% | 6.39% | -13.13% | -1.51% | 10.41% | 9.64% | -0.85% | 3.89% |
Correlation
The correlation between VMBSX and VCOBX is 0.96 - these two move nearly in lockstep. At this level, holding both provides almost no diversification benefit. If you already own one, adding the other does little to reduce portfolio risk.
| Correlation | |
|---|---|
Correlation (1Y) Calculated over the trailing 1-year period | 0.96 |
Correlation (3Y) Calculated over the trailing 3-year period | 0.97 |
Correlation (5Y) Calculated over the trailing 5-year period | 0.95 |
Correlation (10Y) Calculated over the trailing 10-year period | 0.89 |
Correlation (All Time) Calculated using the full available price history since Mar 31, 2016 | 0.88 |
The correlation between VMBSX and VCOBX has been stable across timeframes, ranging from 0.88 to 0.97 - a consistent structural relationship.
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Return for Risk
VMBSX vs. VCOBX — Risk / Return Rank
VMBSX
VCOBX
VMBSX vs. VCOBX - 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 Vanguard Core Bond Fund Admiral Shares (VCOBX). 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.
| VMBSX | VCOBX | Difference | |
|---|---|---|---|
| Sharpe ratioReturn per unit of total volatility | +0.26 | ||
| Sortino ratioReturn per unit of downside risk | +0.39 | ||
| Omega ratioGain probability vs. loss probability | 1.33 | 1.27 | +0.05 |
| Calmar ratioReturn relative to maximum drawdown | 2.54 | 2.13 | +0.41 |
| Martin ratioReturn relative to average drawdown | 8.52 | 6.33 | +2.19 |
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month. | |||
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Sharpe Ratios by Period
| VMBSX | VCOBX | Difference | |
|---|---|---|---|
Sharpe Ratio (1Y)Calculated over the trailing 1-year period | 1.78 | 1.52 | +0.26 |
Sharpe Ratio (5Y)Calculated over the trailing 5-year period | 0.07 | 0.10 | -0.02 |
Sharpe Ratio (10Y)Calculated over the trailing 10-year period | 0.38 | 0.46 | -0.08 |
Sharpe Ratio (All Time)Calculated using the full available price history | 0.58 | 0.48 | +0.10 |
Drawdowns
VMBSX vs. VCOBX - Drawdown Comparison
The maximum VMBSX drawdown since its inception was -17.44%, roughly equal to the maximum VCOBX drawdown of -18.14%. Use the drawdown chart below to compare losses from any high point for VMBSX and VCOBX.
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Drawdown Indicators
| VMBSX | VCOBX | Difference | |
|---|---|---|---|
Max DrawdownLargest peak-to-trough decline | -17.44% | -18.14% | +0.70% |
Max Drawdown (1Y)Largest decline over 1 year | -2.67% | -2.62% | -0.05% |
Max Drawdown (3Y)Largest decline over 3 years | -7.53% | -5.63% | -1.90% |
Max Drawdown (5Y)Largest decline over 5 years | -17.12% | -18.03% | +0.91% |
Max Drawdown (10Y)Largest decline over 10 years | -17.44% | -18.14% | +0.70% |
Current DrawdownCurrent decline from peak | -1.43% | -1.41% | -0.02% |
Average DrawdownAverage peak-to-trough decline | -2.48% | -4.18% | +1.70% |
Ulcer IndexDepth and duration of drawdowns from previous peaks | 0.79% | 0.88% | -0.09% |
Volatility
VMBSX vs. VCOBX - Volatility Comparison
Vanguard Mortgage-Backed Securities Index Fund Admiral Shares (VMBSX) has a higher volatility of 1.43% compared to Vanguard Core Bond Fund Admiral Shares (VCOBX) at 1.29%. This indicates that VMBSX's price experiences larger fluctuations and is considered to be riskier than VCOBX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.
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Volatility by Period
| VMBSX | VCOBX | Difference | |
|---|---|---|---|
Volatility (1M)Calculated over the trailing 1-month period | 1.43% | 1.29% | +0.14% |
Volatility (6M)Calculated over the trailing 6-month period | 2.72% | 2.63% | +0.09% |
Volatility (1Y)Calculated over the trailing 1-year period | 3.82% | 3.67% | +0.15% |
Volatility (5Y)Calculated over the trailing 5-year period, annualized | 6.40% | 5.78% | +0.62% |
Volatility (10Y)Calculated over the trailing 10-year period, annualized | 4.86% | 4.76% | +0.10% |
VMBSX vs. VCOBX - Expense Ratio Comparison
VMBSX has a 0.07% expense ratio, which is lower than VCOBX's 0.10% 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
VMBSX vs. VCOBX - Dividend Comparison
VMBSX's dividend yield for the trailing twelve months is around 4.17%, less than VCOBX's 4.74% yield.
| Position | TTM | 2025 | 2024 | 2023 | 2022 | 2021 | 2020 | 2019 | 2018 | 2017 | 2016 | 2015 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
VCOBX Vanguard Core Bond Fund Admiral Shares | 4.74% | 4.80% | 5.04% | 4.44% | 3.01% | 1.23% | 3.09% | 3.08% | 3.10% | 2.20% | 2.29% | 0.00% |
VMBSX Vanguard Mortgage-Backed Securities Index Fund Admiral Shares | 4.17% | 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
With a correlation of 0.96, VMBSX and VCOBX 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.
VMBSX has higher volatility (1.43%) compared to VCOBX (1.29%). In terms of maximum drawdown, VMBSX dropped -17.44% vs VCOBX's -18.14%.
VMBSX currently has the higher Sharpe Ratio (1.78 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.
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