Once you have selected your accounts, the next step is deciding what to buy inside them. For the beginner, the goal is simplicity, low costs, and broad diversification. This is typically achieved through low-cost index funds.

Index Fund Investing: The Simple Path

An index fund is a type of mutual fund or Exchange-Traded Fund (ETF) designed to mimic the performance of a specific market benchmark, such as the S&P 500. Instead of paying a "star" fund manager to try (and usually fail) to beat the market, you simply own the whole market.

Why Index Funds?

Low Fees: Actively managed funds often charge 1% or more in expense ratios. Many index funds at Vanguard or Fidelity charge less than 0.05% . Over 30 years, this difference can amount to hundreds of thousands of dollars.
Diversification: A single Total Stock Market index fund allows you to own a piece of thousands of companies, protecting you if any one company goes bankrupt.
Tax Efficiency: Index funds trade stocks infrequently, meaning they generate fewer capital gains distributions, which is vital for taxable brokerage accounts .

Asset Location: Putting Assets in Their Place

Asset allocation is the mix of stocks and bonds you own. Asset location is the strategy of deciding which account holds which asset. As Fidelity notes, "Where you put your investments... can make a major difference in how much you can earn, after tax" .

The Tax-Advantaged Scale

Some investments are "tax-inefficient," meaning they generate a lot of taxable income every year. Others are "tax-efficient."

Investment Type	Tax Efficiency	Recommended Location
Bonds / Bond Funds	Low (Interest is taxed at high ordinary rates)	Tax-Deferred (401k/IRA)
REITs (Real Estate)	Low (Dividends are usually taxed as ordinary income)	Tax-Deferred (401k/IRA)
Stock Index Funds	High (Low turnover, qualified dividends)	Taxable Brokerage
Municipal Bonds	High (Interest is often federal tax-free)	Taxable Brokerage

By placing bonds in your 401(k) and stocks in your taxable account, you shield the bond interest from taxes while allowing your stocks to grow with the benefit of lower long-term capital gains rates.

Tax-Loss Harvesting: Turning Lemons into Lemonade

In a taxable brokerage account, you can use a strategy called tax-loss harvesting to lower your tax bill. This involves selling an investment that has lost value to "realize" the loss. You can use this loss to offset any capital gains you've made. If your losses exceed your gains, you can use up to $3,000 of the excess to offset your ordinary income .

The Step-by-Step Guide to Tax-Loss Harvesting

Identify a Loss: You bought Fund A for $10,000, and it is now worth $8,000.
Sell Fund A: You now have a $2,000 realized loss.
Buy Fund B: Immediately buy a "similar but not substantially identical" fund (e.g., sell an S&P 500 fund and buy a Total Stock Market fund) to stay invested in the market .
Wait 30 Days: Avoid the "Wash Sale Rule," which prevents you from claiming the loss if you buy the same fund back within 30 days.
Report the Loss: Use the $2,000 loss to cancel out $2,000 of gains elsewhere, or reduce your taxable income.

The Role of Taxable Brokerage Accounts

While tax-advantaged accounts are great, they have "lock-up" periods. For a FIRE practitioner, the taxable brokerage account is the "Bridge Account." It provides the liquidity needed to live on before you can access your 401(k) or IRA. There are no limits on how much you can contribute, and if you manage it well using index funds and tax-loss harvesting, it can be remarkably tax-efficient.

Net Investment Income Tax (NIIT)

Be aware that if your income is high, you may face the NIIT. This is a 3.8% surtax on interest, dividends, and capital gains if your income exceeds $200,000 (single) or $250,000 (married) . Keeping your taxable income low through 401(k) and HSA contributions is the best way to avoid this "success tax."

Pro-Tip: Use Tools to Stay on Track

Brokerages like Vanguard offer "Portfolio Watch" and "Portfolio Testers" to help you see how your asset mix is diversified and how expense ratios are affecting your long-term costs . Regularly auditing your portfolio for high-fee funds is one of the easiest ways to accelerate your path to FIRE.