The 3-fund portfolio is the simplest investment plan that actually works: three low-cost index funds covering US stocks, international stocks and bonds, rebalanced once a year. It beats most professional investors, costs almost nothing, and takes an hour a year to maintain. This guide shows how to build one and how to adjust it as you age.

The Three Funds

Fund one is a total US stock market index fund, covering every listed American company. Fund two is a total international stock index fund, covering developed and emerging markets outside the US. Fund three is a total bond market index fund, covering government and corporate bonds. Together they own the whole investable world, and the only decision you make is the split between them.

Choosing Your Allocation

A common starting point is 60% US stocks, 20% international stocks and 20% bonds, which suits a saver in their thirties with decades ahead. Younger savers can hold 80-90% stocks, while those near retirement shift toward 50-60% stocks. The classic rule is to hold your age in bonds: a 40-year-old holds 40% bonds, a 30-year-old holds 30%. Adjust to your risk tolerance, but never hold zero bonds: even aggressive savers benefit from the stability.

Where to Hold Each Fund

Hold bonds in tax-advantaged retirement accounts, where their interest is sheltered from annual tax. Hold international stocks in taxable accounts, where you can claim the foreign tax credit. Hold US stocks anywhere. This placement, called asset location, can add 0.1-0.3% a year to your return without any extra risk. It is a small optimisation, but over decades it compounds into real money.

Rebalancing Once a Year

Once a year, check your allocation and sell the funds that grew past their target to buy the ones that lagged. This forces you to sell high and buy low, which is the discipline most investors lack. Rebalance inside retirement accounts to avoid tax, and use new contributions to rebalance when possible. Never rebalance in a panic during a crash: wait for your annual date and follow the plan.

Why Simplicity Wins

Complexity is the enemy of consistency: a portfolio with fifteen funds gets neglected, while a three-fund portfolio gets maintained. The 3-fund approach also makes it easy to see what you own and why, which keeps you calm during market falls. If you want to add a tilt, such as small-cap value or real estate, add one fund and keep the total under five. Simplicity is not a compromise; it is the strategy.

Adding a Fourth Fund

Some investors add a fourth fund to the 3-fund portfolio, usually small-cap value, real estate, or inflation-protected bonds, to tilt the portfolio toward a factor they believe in. The tilt can add return, but it also adds complexity and tracking error, and the benefit is uncertain. If you add a tilt, keep it small, under 10% of the portfolio, and hold it for at least a decade, because factor premiums take years to appear. The 3-fund portfolio works without any tilt, and the tilt is an optimisation, not a necessity. Simplicity is the strategy, and the fourth fund is the exception.

Key Takeaways

- Three funds cover the whole investable world: US stocks, international stocks, bonds - A common split is 60% US, 20% international, 20% bonds - Hold bonds in retirement accounts and international stocks in taxable accounts - Rebalance once a year to force selling high and buying low

Frequently Asked Questions

What is a 3-fund portfolio? A portfolio of three low-cost index funds: total US stocks, total international stocks, and total bonds. It is the simplest investment plan that beats most professionals.

Three funds, one hour a year, and a plan you can stick to through every crash. Simplicity is the strategy.