Building a Portfolio with Low-Cost Index Funds

The goal of index fund portfolio construction is to capture the returns of the entire global market at the lowest possible cost. You do not need to pick stocks, time markets, or predict which sectors will outperform. You need three funds and the discipline to keep buying them.

For how to decide your overall stock/bond split before choosing specific funds, see Asset Allocation Guide.

The Three-Fund Portfolio

The three-fund portfolio, popularized by the Bogleheads community (named after Vanguard founder John Bogle), captures the entire investable world:

Fund Slot	What It Captures	Vanguard	Fidelity	Schwab
US Total Market	~4,000 US stocks, all sizes	VTSAX / VTI (0.03%)	FSKAX / FZROX (0.015% / 0.00%)	SWTSX (0.03%)
International Total Market	~8,000 non-US stocks, developed + emerging	VTIAX / VXUS (0.07%)	FTIHX / FZILX (0.06% / 0.00%)	SWISX (0.06%)
US Total Bond Market	~10,000 investment-grade bonds	VBTLX / BND (0.03%)	FXNAX (0.025%)	SWAGX (0.04%)

These three funds give you exposure to virtually every publicly traded security on earth, for a blended expense ratio of approximately 0.04%. That is $40 per year on a $100,000 portfolio.

Allocation: How Much in Each?

There is no universally correct allocation, but here are well-reasoned starting points:

For Aggressive Early Retirement Savers (20+ Years to Retirement)

Fund	Allocation	Rationale
US Total Market	60%	Core growth engine; US has been ~60% of global market cap
International	30%	Diversification; reduces single-country risk
Bonds	10%	Minimal drag; provides rebalancing fuel during crashes

For Mid-Accumulation (10-20 Years to Retirement)

Fund	Allocation	Rationale
US Total Market	50%	Still growth-oriented
International	25%	Maintained diversification
Bonds	25%	Increased stability as portfolio grows larger

For Near-Retirement (Under 10 Years)

Fund	Allocation	Rationale
US Total Market	40%	Reduced but still meaningful equity exposure
International	20%	Maintained diversification
Bonds	40%	Protecting the portfolio you will soon live on

Why Not Just 100% Stocks?

It is tempting to hold 100% equities for maximum growth, especially when retirement is decades away. The issue is behavioural, not mathematical:

• In 2008-2009, the S&P 500 fell 56.8% from peak to trough. A $500,000 portfolio became $216,000.
• In the 2020 COVID crash, markets fell 34% in 23 trading days.
• In 2022, both stocks and bonds fell simultaneously — something that rarely happens.

A small bond allocation (10-20%) gives you something to sell and rebalance from during crashes, which is precisely when you should be buying stocks. The investor who sold bonds to buy stocks in March 2009 earned returns that more than compensated for bonds' lower long-term return.

Total Market vs. S&P 500

Both are excellent choices, and over long periods they are nearly identical. However, total market funds are slightly preferable:

• They include mid-cap and small-cap stocks, which have historically produced slightly higher returns
• They are more diversified (4,000 vs. 500 stocks)
• The difference in expense ratio is negligible (0.03% vs. 0.03%)

If your 401(k) only offers an S&P 500 fund, that is perfectly fine. Do not agonise over this distinction.

Rebalancing

Over time, stocks will outpace bonds, pushing your allocation away from your target. Rebalancing restores it:

• Frequency: Once per year is sufficient. More frequent rebalancing adds transaction costs and tax events without meaningful benefit.
• Method: In accumulation, rebalance by directing new contributions to the underweight asset class. This avoids selling (and triggering taxes).
• Bands: Alternatively, only rebalance when an asset class drifts more than 5 percentage points from its target (e.g., bonds fall below 5% when target is 10%).
• Location: Rebalance in tax-advantaged accounts first to avoid capital gains taxes.

What NOT to Buy

• Sector funds (technology, healthcare, energy): You already own these sectors through the total market fund. Sector funds add cost and concentration risk.
• Dividend-focused funds: Dividend investing is a psychological preference, not a mathematical advantage. Total return is what matters.
• Target-date funds in taxable accounts: Their bond holdings create tax drag. Use them only in 401(k)s or IRAs.
• Alternative investments (gold, commodities, REITs, crypto): These add complexity and cost. If you feel strongly, limit them to under 5% of your portfolio.
• Smart beta / factor funds: These charge higher fees for strategies that may not persist. The evidence is mixed and the costs are certain.

Asset Location: Which Fund Goes Where?

Asset location — placing tax-inefficient assets in tax-advantaged accounts — can add 0.1-0.5% annually in after-tax returns. See Account Type Strategy for Early Retirement for the full framework, but the summary is:

Fund	Best Account Type	Reason
Bonds	401(k) / Traditional IRA	Bond interest is taxed as ordinary income
International stocks	Taxable brokerage	Foreign tax credit is only available in taxable accounts
US stocks	Any account	Tax-efficient due to low turnover and qualified dividends

Getting Started

1. Open accounts at Vanguard, Fidelity, or Schwab (all are excellent; pick one and stay)
2. Set up automatic monthly contributions
3. Buy the three funds in your target allocation
4. Set a calendar reminder to rebalance once per year
5. Ignore financial news, market predictions, and anyone selling complexity

The single most important thing is to start. A perfect portfolio bought next year loses to an imperfect portfolio bought today.

Related Articles

• Back to hub: Index Fund Investing for Early Retirement
• Why Expense Ratios Are the Investor's Biggest Controllable Cost
• Account Type Strategy for Early Retirement
• Low-Cost Index Fund Investing — existing introductory article
• Introduction to Index Funds and ETFs — existing article