Warren Buffett's advice for 99% of investors: buy a low-cost S&P 500 index fund and never sell. Why? Because over 15-year periods, index funds beat 92% of actively managed funds. They're simpler, cheaper, and more effective than trying to pick winning stocks or fund managers.
What is an Index Fund?
An index fund is an investment fund designed to replicate the performance of a specific market index. It owns the same stocks as the index, in the same proportions.
How Index Funds Work
Example: S&P 500 (500 largest US companies)
The fund buys shares of Apple, Microsoft, Amazon, etc. in the exact percentages they represent in the S&P 500
When index composition changes (companies added/removed), the fund adjusts holdings
You buy 1 share of the index fund = instant ownership of all 500 companies
- Apple: 7.1%
- Microsoft: 6.8%
- Amazon: 3.4%
- Nvidia: 3.2%
- Alphabet (Google): 2.8%
- Meta (Facebook): 2.3%
- Tesla: 1.9%
- Berkshire Hathaway: 1.7%
- + 492 more companies
You instantly own tiny fractions of all 500 companies. Apple's stock goes up? Your fund goes up. Total diversification in one purchase.
Don't look for the needle in the haystack. Just buy the haystack! Index funds let you own the entire market at the lowest cost.
— John Bogle (Founder of Vanguard, Creator of First Index Fund)
Why Index Funds Beat Active Funds
Active funds try to beat the market by picking "winning" stocks. Index funds simply match the market. Counterintuitively, matching the market beats trying to beat it.
Active Funds (Trying to Beat the Market)
Professional managers research stocks, pick winners, avoid losers. Frequent trading.
- Expense ratio: 0.5-1.5% annually
- Trading costs: Hidden but significant
- Load fees: 3-5% upfront (some funds)
- 15-year success rate: 8% beat their index
- 20-year success rate: 5% beat their index
- After fees, most underperform
Index Funds (Matching the Market)
Automatically buy all stocks in an index. No manager decisions. Minimal trading.
- Expense ratio: 0.03-0.20% annually
- Trading costs: Nearly zero
- No load fees
- Matches market return (S&P 500: ~10% historically)
- Beats 92% of active funds over 15 years
- Guaranteed average, which is above average after fees
The Math: Why Fees Matter Enormously
- Gross return: 10%
- After fees: 9.97%
- Final value: $174,207
- Total fees paid: $765
- Gross return: 10% (assuming it matches market)
- After fees: 9.0%
- Final value: $132,677
- Total fees paid: $42,295
Difference: $41,530 lost to fees!
A 1% higher fee doesn't sound like much, but over 30 years it costs you 24% of your wealth. Index funds' low fees are their superpower.
Types of Index Funds
Index funds come in two structures: Mutual Funds and ETFs (Exchange-Traded Funds). Both track indexes, but differ in how you buy/sell them.
Index Mutual Funds vs Index ETFs
| Feature | Index Mutual Fund | Index ETF |
|---|---|---|
| How You Buy | Once per day (after market close) | Anytime during market hours |
| Minimum Investment | $1,000-3,000 (often waived) | Price of 1 share (~$50-500) |
| Trading Fees | None (typically) | $0 at most brokers |
| Tax Efficiency | Good | Better (lower capital gains) |
| Auto-Invest | Easy (set $ amount) | Harder (need fractional shares) |
| Best For | 401(k)s, automatic contributions | Brokerage accounts, flexibility |
Best Index Funds for Beginners (2025)
S&P 500 Index Funds (Most Popular)
VOO - Vanguard S&P 500 ETFBEST OVERALL
Expense Ratio: 0.03% ($3 per $10k)
Price: ~$450/share
Dividends: ~1.5% yield, quarterly
Assets Under Management: $500+ billion
Where to Buy: Any major broker
Minimum: 1 share (or fractional)
SPY - SPDR S&P 500 ETF
Expense Ratio: 0.09% ($9 per $10k)
Price: ~$500/share
Dividends: ~1.5% yield, quarterly
Assets Under Management: $400+ billion
Unique: Most traded ETF globally
Best For: Active traders (high liquidity)
IVV - iShares Core S&P 500 ETF
Expense Ratio: 0.03% ($3 per $10k)
Price: ~$525/share
Dividends: ~1.5% yield, quarterly
Assets Under Management: $400+ billion
Provider: BlackRock (iShares)
Best For: Identical to VOO, preference choice
Total Market Index Funds (Even More Diversified)
VTI - Vanguard Total Stock Market ETFMOST DIVERSIFIED
Holdings: 3,600+ US companies (all sizes)
Expense Ratio: 0.03% ($3 per $10k)
Price: ~$260/share
Includes: Large, mid, small cap stocks
Allocation: 83% large, 14% mid, 3% small
Best For: Total US market exposure
ITOT - iShares Core S&P Total US Stock Market ETF
Holdings: 3,500+ US companies
Expense Ratio: 0.03%
Price: ~$115/share (lower price point)
Provider: BlackRock (iShares)
Best For: VTI alternative, lower share price
Global Market Index Funds (International Diversification)
VT - Vanguard Total World Stock ETF
Holdings: 9,000+ stocks globally
Expense Ratio: 0.07% ($7 per $10k)
Price: ~$105/share
Countries: 50+ countries
Best For: Ultimate diversification, global exposure
Benefit: Auto-adjusts to global market cap
Best Index Mutual Funds (For 401(k)s)
If your employer 401(k) doesn't offer ETFs, look for these low-cost index mutual funds:
- Tracks: S&P 500
- Expense ratio: 0.04%
- Minimum: $3,000 (often waived in 401(k)s)
- Tracks: S&P 500
- Expense ratio: 0.015% (lowest available)
- Minimum: $0
- Tracks: Total US market (3,600+ stocks)
- Expense ratio: 0.04%
- Minimum: $3,000 (waived in 401(k)s)
- Tracks: Total US market
- Expense ratio: 0.015%
- Minimum: $0
How to Invest in Index Funds
Step-by-Step: Buying Your First Index Fund
Fidelity, Schwab, or Vanguard (all offer $0 commissions, fractional shares)
Transfer money from your bank ($100-1,000+ to start)
Beginner recommendation: VOO (S&P 500) or VTI (Total Market)
- Search for ticker: "VOO"
- Click "Buy"
- Enter dollar amount (e.g., $500) or number of shares
- Order type: "Market order" (simplest)
- Confirm and submit
Invest $100-500/month automatically. This is the key to wealth building.
- 100% VTI or VOO
- Rationale: 40 years to retirement, maximize growth
- 70% VTI (US stocks)
- 30% BND (US bonds)
- Rationale: Still growth-focused but adding stability
- 40% VTI (US stocks)
- 20% VXUS (International stocks)
- 40% BND (US bonds)
- Rationale: Balanced, diversified globally, reduced volatility
Common Questions
Should I buy S&P 500 (VOO) or Total Market (VTI)?
Performance is nearly identical. Over the past 20 years, they've differed by less than 0.5% annually. VOO = 500 companies. VTI = 3,600 companies (includes mid/small caps). Both are excellent. Pick one and don't overthink it.
Can I just invest in one index fund forever?
Yes! 100% VTI or 100% VT (world index) is a valid lifetime strategy. Warren Buffett's will instructs his trustee to invest in a single S&P 500 index fund. Simplicity works.
What about sector-specific index funds (tech, healthcare)?
Avoid for most investors. Sector funds concentrate risk. The S&P 500 already includes tech (Apple, Microsoft, Nvidia). If tech does well, VOO does well. Don't overthink it with sector bets.
Should I buy when the market is down or up?
Always. Time in the market beats timing the market. Dollar-cost averaging (investing the same amount monthly) removes emotion. Buy when it's up, buy when it's down. Consistency wins.
Conclusion: The Only Investment Guide You Need
Index fund investing isn't sexy. It won't make you rich overnight. But over 20-40 years, it's the most reliable path to wealth for 99% of investors. No stock picking. No fund manager fees. Just consistent contributions to a low-cost index fund.
Both large and small investors should stick with low-cost index funds. My advice to the trustee of my estate: Put 90% in a very low-cost S&P 500 index fund and 10% in short-term government bonds.
— Warren Buffett (2013 Shareholder Letter)
Your Index Fund Action Plan
If you invest $500/month in an S&P 500 index fund (VOO) starting at age 25:
- By age 35: $91,473
- By age 45: $294,910
- By age 55: $745,514
- By age 65: $1,745,503
You contributed $240,000 total. The other $1.5 million? That's compounding at work. Index funds + time + consistency = wealth.
Continue Your Learning Journey
Ready to build your index fund portfolio? Read these next:
- How to Open Your First Brokerage Account - Get started in 30 minutes
- Asset Allocation 101 - How to split between stocks and bonds
- How Much Money Do You Need to Start Investing? - Start with fractional shares for just $1
- How to Start Investing in Stocks: Complete Guide - The full beginner roadmap
- 5 Investing Mistakes That Cost Beginners Thousands - Avoid these common pitfalls