Individual bonds vs a bond fund

The major factors  in deciding between owning a bond fund versus individual bonds are:  diversification,  convenience,  costs, and  control over maturity. There is a common belief (promoted by Suze Orman, among others) that owning individual bonds is less risky than a bond fund, but this is incorrect. Duration is an essential attribute for understanding the riskiness of a fund or ladder over time. There's also an important distinction between owning a ladder of individual bonds designed to meet specific future liabilities, and holding a rolling bond ladder.

Diversification
Diversification is important for bonds, as it is for all asset classes. The argument against an investor ever owning individual corporate or municipal bonds (even in a ladder) is that the effect of a single default (such as a corporation or city brought down by fraud), even if unlikely, could be devastating to the investor's portfolio. By contrast, bond funds allow extremely broad diversification at a very low cost.

A ladder of individual bonds generally includes between 10 and a couple dozen bonds. That means that each bond represents 2.5% to 10% of a portfolio. By contrast Total Bond owns 3855 different bonds, and Intermediate Term Tax Exempt owns 1971. So, the failure (default) of any one bond has a minuscule effect on the fund.

The only exceptions are Treasury bonds (including TIPS). Because all Treasury bonds are explicitly backed by the US government, they have the highest possible credit rating. They also all have the same issuer. There is no diversification benefit from owning a Treasury bond fund instead of individual Treasury bonds.

Convenience
Investors in a bond fund can buy or sell additional shares at any time in any quantity. There is usually no transaction fee for buying or selling additional shares. With individual bonds, purchases on the primary market may only be made on the pre-set issuer schedule (e.g., every few months for TIPS). Purchases on the secondary market are generally subject to a commission and one always pays a bid/ask spread, which can be substantial. Also, individual bond purchases are only available in increments of $1,000 (and more often $5,000 or $10,000).

Bond funds offer automatic dividend reinvestment. While you are in your accumulation phase, it is far more convenient to have dividends automatically reinvested. Even after beginning to spend your holdings, it is generally simpler to have bond funds automatically reinvest dividends and then just sell a fixed amount of the fund monthly or quarterly. By contrast, there is no simple way to reinvest small amounts into individual bonds. It is also far more convenient to rebalance between a bond fund and other assets in your portfolio.

Taxes are simpler for bond funds. If you invest in a bond fund in a taxable account, you receive tax forms from the bond fund company. If you have a portfolio of individual bonds, you receive tax forms from TreasuryDirect or your brokerage account listing the tax-related items for each bond. It's easier to figure out the tax reporting for one bond fund versus many individual bonds. Also, owners of individual TIPS owe a tax on phantom income that they do not receive. This is not an issue with TIPS funds.

Costs
The costs associated with owning bonds are commissions, bid/ask spreads, and management fees. Primary purchases of bonds (such as at a TIPS auction) generally do not incur commissions or bid/ask spreads. Purchases and sales on a secondary market can have substantial commissions and bid/ask spreads, particularly on less liquid bonds like municipals and corporates. With the exception of primary purchases of Treasury bonds and TIPS, bond funds pay much lower bid/ask spreads on their bond transactions, giving them a significant cost advantage over regular investors purchasing individual bonds.

There is no management fee for holding a portfolio of individual bonds. However, there is an opportunity cost associated with the time to do so. If you enjoy purchasing TIPS in auction, than this time is really a consumption item rather than an expense. If tracking auction dates and the shape of the yield curve doesn't seem like fun, than it should be treated as a real cost. For example, holding $100,000 of VAIPX (Vanguard Inflation-Protected Securities Fund Admiral) costs $110 per year (with an expense ratio of 0.11%). If you value your time at $55 an hour, it is more cost effective to use this fund than hold your own portfolio of bonds if it takes you more than 2 hours a year to manage your portfolio.

Control over maturity
By managing your own portfolio of bonds, you can either pick the average duration you want or "ride" the yield curve to pick up bonds that are "cheap" compared to the  ladder overall, and allow your duration to fluctuate with your purchases. In either case, you are in control. With a bond fund, the duration is designed not to move more than a year or two and is managed by the fund.

However, investors need to consider who is in the best position to find bonds that are slightly under-priced, you or a dozen expert bond analysts at a fund company whose only job it is to follow the bond market?

Also, if you'd like a shorter duration than offered by a bond fund, it is easy to shorten it by putting a portion of the money in a money market fund. For example, the Vanguard municipal bond fund for New York has an average maturity of 11.1 years. You can approximately halve that by holding half of your money in that fund and half in the New York Tax Exempt Money Market.

Bond funds are no riskier than individual bonds
It has been regularly argued on the Bogleheads forum that a bond fund is risky because of NAV fluctuations. For example, the NAV for Vanguard Inflation Protected Securities fell 20.4% from peak to trough in 2008. Instead, it is said, investors should hold individual bonds, which can always be redeemed at face value by holding until maturity.

This argument is wrong because the individual bonds in a bond fund react to the market identically to the individual bonds held in a personal portfolio. You can see this by manually calculating a NAV for your own portfolio of individual bonds, and watching its daily fluctuations. The key thought is that although bond funds do have volatility, they are exactly as volatile as a rolling bond ladder with the same duration. On a Bogleheads Forum post, tfb made this explicit with the following example:

"After you create your TIPS ladder, call this ladder 'My TIPS Fund.' Create some imaginary shares and calculate the NAV for your fund. When one bond matures, for which you receive the full guaranteed value and real yield, you take the cash, divide by the NAV at that time, and reduce the number of shares you still own in My TIPS Fund. Now, it's as if you just sold some shares from My TIPS Fund at the current NAV. Let's say the NAV is lower than the initial NAV. Did you just suffer a loss? Or did you receive the full guaranteed value and real yield from the matured bond? You see it's just a matter of framing. The substance remains exactly the same."

At any moment after buying a bond fund, you can always be assured of getting your principal back. Doing so requires selling the fund and buying a zero-coupon bond with the face value of your principal. Such a bond will always be available, because if the fund's NAV is down, yields will have gone up a commensurate amount. On average (with a typical yield curve), the bond will have a maturity equal to the duration of the TIPS fund. (A regular TIPS bond would also serve the same purpose, but a zero coupon bond makes the calculation simpler, because the duration equals the maturity.)

Similarly, at any moment after setting up a bond ladder, you can always be assured of getting your principal back. There are two ways of doing it. One, let the whole ladder expire, in which case you have to wait as long as the longest bond. Two, sell all of the bonds in the ladder, and buy a single zero-coupon bond with a face value equal to the original principal. On average, the second method will get you your principal back in half the time as the first method. (I.e., with an evenly distributed bond ladder and a normal yield curve, duration will be about half the maximum bond term.)

These ideas were discussed on these threads:
 * How long before a bond fund will at least return principle?
 * TIPS Tip

Duration
It's useful to focus on the duration of your bond fund, such as the Vanguard TIPS Fund, which currently has a duration of 5.8 years. William Bernstein provides an insightful definition of duration as the "point of indifference" for the owner of a bond fund in dealing with interest rate changes. If interest rates rise after purchasing a bond fund, the NAV of the fund falls, which hurts the investor. However, the dividends that the bond fund throws off can now be reinvested at a higher rate. The duration is the length of time that an investor needs to hold the fund for the increased yields to compensate for the decrease in NAV. In that sense, the duration represents the length of time it could take, in the worst case, to break even on a bond fund. So, you should always hold bond funds with a duration shorter than the expected need for your money.

Of course, as discussed above, this definition of duration applies equally to bond funds and to an individual portfolio of bonds.

Rolling vs. non-rolling bond ladders
If you need to satisfy date-certain future liabilities, a non-rolling ladder of individual bonds is superior to a bond fund. For example, if you commit to make a $10,000 a year payment to a charity for five years, the most effective way to invest for that is to buy 5 zero-coupon bonds, one maturing each year. A non-rolling bond ladder has a sharply decreasing average duration, and means that interest rate shifts have no impact on your investments.

However, most bond ladders are "rolling", because they are not designed to deal with date-certain future liabilities. They are created with a specific average duration, and when the oldest bond comes due, a new long-dated bond is purchased to replace it. A rolling ladder of this kind can and should be directly compared with a bond fund using the criteria above.

As advocated by Zvi Bodie, some people aim to fund their retirement by purchasing a ladder of individual TIPS with durations of 1 to 30 years (although note that new 30 year TIPS are no longer being issued). The idea is to avoid the volatility of the underlying bonds by always holding them to maturity, so as to avoid having to sell the fund at moments when high yields have caused the NAV to drop.

If you are planning to reinvest (i.e, rollover) some of the annual redemption into new individual TIPS bonds, then you have gained nothing by using a rolling ladder over a fund. Because not rolling over the whole bond at the (hypothetically) very high yield has an identical opportunity cost to selling a portion of your fund at the (hypothetically) very low NAV. Another issue with this approach is how to deal with the longevity risk if you outlive your ladder.

Thus, the distinction between a non-rolling ladder (designed to meet date-certain future liabilities) and a rolling ladder (which essentially represents a personal bond fund) is much more important than the difference between a rolling ladder and a bond fund.

Links

 * Taxable Bond Funds and Individual Bonds Vanguard Investment Counseling and Research
 * Municipal Bond Funds and Individual Bonds Vanguard Investment Counseling and Research