Regardless of your investment objective, bonds often play a significant role. Some funds, like the Vanguard Total Bond Market ETF, are designed to give access to a wide variety of income-generating vehicles while minimizing costs. Many bond funds are suitable as core holdings for investors. Here, we take a look at five of the top bond funds for long-term investors.

1. Fidelity Total Bond Fund (FTBFX)

The Fidelity Total Bond Fund seeks to provide investors with high levels of current income. The fund uses the Bloomberg Barclays U.S. Universal Bond Index in guiding its allocation decisions and as a benchmark index. The fund invests around 80% of its assets in a wide range of debt securities. It then invests about 20% of its assets in debt securities with lower credit ratings. These lower-quality debt securities have higher risks than investment-grade bonds, but they also offer higher yields. The fund also engages in derivatives trading, which allows increased leverage but also contains specific types of risk. The derivatives include trading swaps, options, and futures contracts.

The Fidelity Total Bond Fund had $26.1 billion in assets under management (AUM) with a 30-day Securities and Exchange Commission (SEC) yield of 2.49% as of November 2019. The debt securities in the fund had an average duration of 5.23 years. Historically, the fund displayed low volatility. It had over 82% of its assets in investment-grade bonds, with over 32% allocated to U.S. government bonds. It had a reasonable expense ratio of 0.45%, and there was no minimum investment requirement.

2. Vanguard Total Bond Market ETF (BND)

The Vanguard Total Bond Market ETF provides broad exposure to U.S. investment-grade bonds. As of November 2019, the fund invested around 63% of its assets in U.S. government bonds across all maturities. The remaining 37% was held in other investment-grade bonds. It had a very low expense ratio of 0.035%, which is over 90% below the average expense ratio of funds with similar holdings. Vanguard funds are known for having some of the lowest expense ratios in the industry.

The Vanguard Total Bond Market Fund had $245.5 billion in total net assets ($46.7 billion in the ETF) with an SEC yield of 2.26%. It had 9,010 holdings with an average effective maturity of 8.2 years and an average duration of 6.2 years. Since it is an ETF, there is no minimum initial investment requirement.

3. Dodge & Cox Income Fund (DODIX)

The Dodge & Cox Income Fund seeks to provide a high and stable rate of current income while providing for long-term preservation of capital. Around 80% of assets are in investment-grade securities, with up to 20% placed in debt obligations below investment grade. DODIX is a rather safe core holding, even if it doesn't carry the same brand recognition of Vanguard or BlackRock.

The Dodge & Cox Income Fund had an SEC yield of 2.67% with an expense ratio of 0.42%. It had net assets of $62.3 billion in its portfolio as of September 2019. The fund required a $2,500 initial investment.

4. Metropolitan West Total Return Bond Fund (MWTRX)

The Metropolitan West Total Return Bond Fund is designed to be a core bond fund. Its goal is to outperform the Bloomberg Barclays U.S. Aggregate Bond Index while maintaining a similar risk profile to that index. The Bloomberg Barclays U.S. Aggregate Bond Index tracks investment-grade bonds.

The Metropolitan West Total Return Bond Fund invests in a wide range of fixed-income securities, including derivatives that may be used to hedge risk exposure. The fund had over $79.9 billion in AUM with an SEC yield of 2.04% as of November 2019. It had an expense ratio of 0.67% for the investor shares. The holdings in the portfolio had an average duration of 5.75 years and an average maturity of 7.69 years. The fund required a rather hefty $5,000 initial investment.

5. Loomis Sayles Core Plus Bond Fund (NEFRX)

The Loomis Sayles Core Plus Bond Fund seeks to provide higher total returns by investing in quality corporate and U.S. government bonds. The fund has a higher amount of risk than many other bond funds because it holds fixed-income securities that are high-yield and from emerging markets. It had net assets of $7.43 billion, with an SEC yield of 1.87% as of November 2019.

The Loomis Sayles Core Plus Bond Fund had a somewhat high expense ratio of 0.73%. It must perform better to justify its higher expenses compared to other funds. The holdings in the fund have an effective duration of 6.17 years, with an average maturity of 8.52 years. The fund required a minimum investment of $2,500.