In brief
The Bogleheads three-fund portfolio combines broad U.S. stocks, international stocks, and U.S. investment-grade bonds. A common four-fund version separates international bonds into a fourth sleeve. The fourth fund broadens the bond allocation beyond the United States, but it also adds another holding, another target weight, and another source of tracking difference.
Neither fund count is inherently superior. The decision is whether international fixed income has a defined role in the investor’s plan.
What changes
| Question | Three-fund approach | Four-fund approach |
|---|---|---|
| Equity coverage | Broad U.S. and non-U.S. stocks | Broad U.S. and non-U.S. stocks |
| Bond coverage | U.S. taxable investment-grade market | U.S. plus international investment-grade bonds |
| Number of targets | Three | Four |
| Currency treatment | No dedicated foreign-bond sleeve | Depends on the selected international-bond fund; BNDX states that it hedges currency exposure |
| Main benefit | Simplicity | Broader geographic bond exposure |
| Main cost | U.S.-only bond allocation | More moving parts and another fund expense |
The stock side is the same decision
Both versions can hold the same broad equity building blocks. Vanguard Total Stock Market ETF tracks the CRSP US Total Market Index, while Vanguard Total International Stock ETF tracks the FTSE Global All Cap ex US Index. Splitting global stocks into VTI and VXUS lets the investor choose the U.S./international target rather than accepting a single global fund’s market weights.
This means the fourth fund does not solve an equity-diversification problem. It changes the bond side.
What international bonds add
Vanguard describes BND as broad exposure to the taxable U.S. investment-grade bond market. BNDX tracks a broad index of non-U.S. investment-grade bonds and uses hedging intended to reduce currency fluctuations against the U.S. dollar.
International bonds can diversify issuer, country, interest-rate, and economic exposure. Hedging can reduce one major source of volatility, but it has costs and does not eliminate credit, duration, liquidity, tracking, or market risk.
A worked allocation comparison
Suppose an investor has already chosen 80% stocks and 20% bonds. These are illustrative targets, not recommendations:
| Sleeve | Three funds | Four funds |
|---|---|---|
| U.S. stocks | 48% | 48% |
| International stocks | 32% | 32% |
| U.S. bonds | 20% | 14% |
| International bonds | — | 6% |
The four-fund example does not become more conservative merely because it owns another bond fund. Risk depends on the funds’ duration, credit quality, currency policy, and the total stock/bond mix.
When I would favor three funds
I would favor the simpler structure when the investor wants U.S. bonds to be the stabilizing reserve, has limited fund choices in a workplace plan, or is unlikely to maintain a fourth target consistently. A plan that is easy to execute can be more useful than a theoretically broader plan that is abandoned.
When four funds earns its place
The fourth sleeve is easier to justify when the investor deliberately wants global investment-grade bond exposure, understands the selected fund’s currency policy, and has written rebalancing targets. It should not be added merely because four sounds more diversified than three.
Bottom line
Both structures can provide broad stock and bond exposure. The three-fund version favors simplicity and a U.S.-bond stabilizer; the four-fund version deliberately adds international bonds. Choose the fourth sleeve only when its role is clear enough to justify the extra maintenance.