Bond Fund as Stable Value Mistake
Bond Fund as Stable Value Mistake
A bond fund is not a savings account. Its net asset value (NAV) rises and falls with interest rates and credit conditions. Buying it expecting principal to be safe, then selling when NAV falls, is a formula for losses.
Many investors—especially those older, closer to retirement, and seeking stability—view bond funds as a guaranteed-principal vehicle, similar to a savings account or certificate of deposit. This is fundamentally wrong. A bond fund has no principal guarantee. Its net asset value (NAV, the per-share price) fluctuates daily based on the value of its underlying bonds. When interest rates rise or credit spreads widen, bond fund NAV falls, sometimes dramatically. An investor who bought a bond fund for "safety" at $100 per share and sold it at $85 per share, thinking the principal was guaranteed, has crystallized a loss they never should have taken.
Key takeaways
- Bond fund NAV is the price per share, calculated daily from the value of underlying bonds.
- NAV fluctuates: it can fall 10–20% in a single year if interest rates rise or credit risk increases.
- If you sell shares when NAV is low, you lock in losses. If you hold to maturity of all underlying bonds (impossible in a fund), NAV recovers.
- This is why bond funds are best held when you (a) don't need the money for at least 3–5 years, or (b) intend to hold indefinitely.
- If you need guaranteed principal and income, use Treasury bills (T-bills) or money market funds, not bond funds.
What is NAV, and why does it move?
A bond fund holds hundreds or thousands of individual bonds. The fund values all its bonds at current market prices, adds up their values, subtracts management fees and expenses, and divides by the number of shares outstanding. That is the NAV per share.
If a $100-million bond fund holds 1 million shares, and the bonds are valued at $100 million, the NAV is $100 per share. The next day, interest rates rise. The bonds' market values fall (because bond prices move inversely to rates). The bonds are now valued at $95 million. NAV falls to $95 per share.
This is simple, logical, and disarming to investors who expect bonds to be "safe." The bonds themselves are safe (if held to maturity, most will pay back in full). But the fund's NAV is not safe. NAV is the daily auction price of the bonds in the fund. It moves with the market.
The 2022 bloodbath
In 2022, the Federal Reserve raised rates from 0% to over 4% in the fastest hiking cycle in decades. This devastated bond fund NAVs. The Vanguard Total Bond Market Index (BND) started 2022 at roughly $80 per share and fell to $68 by year-end, a 15% decline. The iShares 20+ Year Treasury ETF (TLT) started at $130 and fell to $70, a 46% decline.
Many investors who had held bonds for "safety" panicked. They sold BND at $68, crystallizing the 15% loss, thinking the damage was permanent. But by mid-2023, as the Fed paused and then considered rate cuts, bond yields stabilized, and NAVs recovered. BND rose back to $80. TLT rose back to $110. An investor who had sold in 2022 crystallized losses that evaporated within six months.
This is the trap: bond fund NAV volatility causes investors to sell at the worst moments, locking in losses that would have reversed if they had held.
Why bond funds are not savings accounts
A savings account or money market fund has a stable NAV (always $1.00 per share) because they hold short-term debt (T-bills, CDs, cash equivalents) with little interest-rate sensitivity. A bond fund holds longer-dated bonds with substantial interest-rate sensitivity. NAV moves because bond prices move.
This is not a flaw of bond funds; it is the nature of bonds. If you hold an individual bond to maturity, you don't see the NAV fluctuation (unless you check the market price daily), and you earn your promised yield. But the market price is still moving. If you held an individual 10-year bond and checked its market value daily, you would see it fall 10–15% when rates rise, exactly like a bond fund does. The volatility is the same; it is just more visible in a fund because you see the NAV daily.
Implications for portfolio allocation
If you truly need principal to be stable, do not use bond funds. Use Treasury bills (Vanguard Treasury Money Market Fund, VMFXX), which maintain a $1.00 NAV by holding only the shortest-duration bonds. Or use a high-yield savings account, which offers similar liquidity and stability. Savings accounts currently yield 4–5%, competitive with Treasury bills, and are FDIC-insured.
But if you are building a portfolio with 30–40% bonds and a 10+ year horizon, bond fund NAV fluctuations are not a problem. They are noise. You buy when bonds are expensive (low yields, after rates have fallen). You hold. Rates eventually rise, NAV falls, you rebalance by selling stocks at inflated prices and buying bonds at depressed NAVs. Over the cycle, you earn steady income and come out ahead.
The problem arises when investors confuse "safe asset" with "stable NAV." Bonds are safer than stocks over decades and in recessions. But their NAV is not stable month-to-month or year-to-year.
Stable value funds in 401k plans
Some 401k plans offer a "stable value" fund, which is distinct from a bond fund. A stable value fund is a wrapped bond portfolio that guarantees a stable price (usually $1.00 per share) by using insurance contracts to smooth NAV. Participants can sell shares to the stable value fund at par ($1.00) even if bond values have fallen. The insurance company absorbs the loss. In return, stable value funds pay lower yields than bond funds (often 2–3%, compared to 3–4% for bond funds).
Stable value funds are designed for participants who plan to leave their jobs and need certainty of principal. They are appropriate in some 401k contexts. But they are not available for retail investors outside of 401k plans, and they carry the cost of the insurance wrapper (lower yields). Most retail investors should not compare bond funds to stable value funds; they should compare bond fund expected returns and volatility to other assets.
The rebalancing trap
A subtle mistake happens when investors treat bond funds as "defensive" holdings within a rebalancing framework. Here is how it goes:
An investor has $500,000: $300,000 stocks, $200,000 bonds (target 60/40). In 2022, stocks fall 15% to $255,000, and bonds fall 15% to $170,000. Portfolio is now $425,000. The investor's allocation is now 60% stocks, 40% bonds (unchanged, coincidentally). But if bonds had fallen more (say 20%), the portfolio becomes $280,000 stocks, $160,000 bonds (64/36). To rebalance back to 60/40, the investor sells stocks and buys bonds.
The error: selling stocks at depressed prices and buying bonds after they have already fallen is opportune. But investors often do the opposite. They see bonds have fallen and assume they are "more dangerous" now, so they sell them, crystallizing losses, and move to cash. This is the opposite of rebalancing discipline.
How it flows
Example: the patient investor vs. the panicker
Investor A: Bought $100,000 of BND at $80/share (1,250 shares) in January 2022.
- By December 2022, NAV fell to $68/share.
- Investor A saw portfolio worth $85,000, down 15%.
- Panicked, sold all shares, locked the loss.
- Moved to cash earning 5%.
Investor B: Bought $100,000 of BND at $80/share (1,250 shares) in January 2022.
- By December 2022, NAV fell to $68/share.
- Investor B saw portfolio worth $85,000, down 15%.
- Held, continued earning 4% yield = $3,400/year.
- By mid-2023, NAV recovered to $80/share.
- Portfolio recovered to $100,000.
- From Jan 2022–Jun 2023, earned ~$7,000 in coupons, plus recovered all principal.
Investor A: -$15,000 (permanent loss) + $5,000 in cash for 6 months = -$10,000 net. Investor B: -$15,000 (temporary loss) + $7,000 coupons + recovered $15,000 = +$7,000 net.
The difference: $17,000 in total wealth, all due to the NAV panic sell.
Who should hold bond funds?
Bond funds make sense for:
- Investors with 3+ year horizons who don't need to touch the capital.
- Rebalancing engines in 60/40 or other strategic portfolios.
- Investors who plan to hold through multiple interest-rate cycles and accept NAV volatility as the cost of diversification.
Bond funds do NOT make sense for:
- Investors who need the capital within 2 years.
- Investors who panic-sell when NAV falls.
- Investors who don't understand the difference between bond market value and bondholder yield.
If you are unsure, use Treasury bills or a high-yield savings account instead. You give up some yield, but you gain certainty and avoid the psychological trap of watching NAV fall and making bad decisions.
Related concepts
Next
The next article examines a different confusion: why certificates of deposit (CDs) and bonds, while superficially similar, have fundamentally different risk profiles and play different roles in a portfolio.