What is an Expense Ratio? An Expense Ratio is the annual fee a mutual fund or ETF charges, expressed as a percentage of assets under management, deducted silently from returns and critically important in FIRE because it compounds against you for decades. Low expense ratios are arguably the single most impactful decision in your portfolio.
Worked example: investing $10,000/year for 30 years at a 7% gross return. In a fund with a 0.03% expense ratio (typical Vanguard index ETF), you end with ~$1,010,000. The same contributions in a fund with a 1.00% expense ratio, common for actively managed funds, end at ~$838,000. The “small” 0.97% fee difference cost you $172,000, or roughly 17% of your final balance.
For FIRE planners, the rule is: prefer total-market or broad-index ETFs with expense ratios under 0.10%, avoid load fees entirely, and audit all 401(k) and retirement plan options for hidden share-class fees. Index funds did not become FIRE’s default asset class by accident, low expenses are mathematical freedom.