📈 What Is the Three-Fund Portfolio?
The three-fund portfolio is an investment strategy using exactly three low-cost index funds to achieve broad diversification across the entire global stock and bond market. Popularized by the Bogleheads community (followers of Vanguard founder John Bogle), it is one of the most evidence-backed approaches to long-term investing available to anyone.
The three funds:
- US Total Stock Market Index Fund — covers all publicly traded US companies (~4,000 stocks)
- International Total Stock Market Index Fund — covers developed and emerging markets outside the US (~8,000 stocks)
- US Total Bond Market Index Fund — covers the entire US investment-grade bond market
Together, these three funds own tiny pieces of essentially every publicly traded company on earth, plus a diversified mix of US bonds. The total expense ratio is typically 0.03–0.10% per year — a fraction of what most actively managed funds charge.
🏦 The Exact Funds to Use (2025)
| Fund Type | Vanguard | Fidelity | Schwab | Expense Ratio |
|---|---|---|---|---|
| US Total Market | VTI / VTSAX | FZROX (0.00%) | SWTSX | 0.00–0.03% |
| International | VXUS / VTIAX | FZILX (0.00%) | SWISX | 0.00–0.11% |
| US Bonds | BND / VBTLX | FXNAX | SWAGX | 0.03% |
Fidelity's ZERO funds (FZROX, FZILX) have literally 0.00% expense ratios — no annual cost whatsoever. The catch: they can only be held at Fidelity and can't be transferred to another brokerage as-is. For investors who plan to stay at Fidelity long-term, they're an extraordinary deal.
⚖️ How to Allocate Between the Three Funds
The right allocation depends on two factors: your time horizon and your risk tolerance. Here are common starting frameworks:
| Investor Type | US Stocks | International | Bonds |
|---|---|---|---|
| Aggressive (20s–30s) | 60% | 30% | 10% |
| Moderate (40s) | 50% | 25% | 25% |
| Conservative (50s+) | 40% | 20% | 40% |
| Target-Date Alternative | Use a single target-date fund — it manages allocation automatically | ||
A common rule of thumb: your age in bonds. A 30-year-old holds 30% bonds. A 55-year-old holds 55% bonds. This is conservative — many financial planners now suggest a more aggressive approach (110 minus your age in stocks) given longer life expectancies and lower bond yields.
Some investors skip international entirely, arguing that large US companies already have global revenue exposure. Others use 30–40% international for true geographic diversification. Both approaches are defensible. The research shows modest benefit to international diversification over very long periods, but significant underperformance vs US-only in recent decades. A 20–30% international allocation is a reasonable middle ground.
🔄 Rebalancing: When and How
Over time, your allocation will drift as different assets grow at different rates. Rebalancing means selling what has grown above your target and buying what has fallen below it — effectively "buy low, sell high" automatically.
Best practices for rebalancing:
- Rebalance once per year at most — more frequent rebalancing in taxable accounts triggers unnecessary capital gains taxes
- Use new contributions to rebalance first — direct new money to underweighted assets instead of selling anything (avoids tax events)
- Set bands, not calendars — rebalance when any asset class drifts more than 5–10% from target, not on a fixed schedule
- In tax-advantaged accounts, rebalance freely — no tax consequences inside an IRA or 401k