What is an index fund and how does it work?

An index fund is a type of investment fund — either a mutual fund or ETF — that tracks a market index like the S&P 500 or the total US stock market. Instead of a fund manager picking individual stocks, the fund simply holds all (or a representative sample) of the stocks in the index. When the index goes up, the fund goes up by a similar amount. Because they're passively managed, index funds charge very low fees — often 0.03% or less per year.

How much money do I need to start investing in index funds?

You can start investing in index funds with as little as $1. Fidelity and Schwab offer fractional shares of ETF index funds starting at $1. Fidelity's zero-expense-ratio mutual funds (FZROX, FZILX) have no minimum investment. Vanguard mutual funds require a $1,000 minimum, but Vanguard ETFs (like VOO) can be purchased as fractional shares through most brokers with $1.

What is a good index fund for beginners?

The Fidelity ZERO Total Market Index Fund (FZROX) and Vanguard S&P 500 ETF (VOO) are excellent starting points for beginners. FZROX has a 0.00% expense ratio and no minimum investment, making it one of the cheapest options available. VOO tracks the S&P 500 (the 500 largest US companies) with a 0.03% expense ratio. Both provide broad US stock market exposure without any complexity.

Are index funds safe?

Index funds carry the same market risk as stocks — they can and do decline during market downturns. The S&P 500 fell 38% in 2008 and 34% in early 2020. However, index funds are considered safer than individual stocks because they're diversified across hundreds or thousands of companies — a single company going bankrupt doesn't wipe out your investment. Historically, the US stock market has recovered from every downturn and delivered positive returns over any 20-year period.

What is an expense ratio and why does it matter?

An expense ratio is the annual fee a fund charges, expressed as a percentage of your investment. A 0.03% expense ratio means you pay $0.30 per year per $1,000 invested. Over time, even small differences in expense ratios compound significantly. $10,000 invested over 30 years at 10% annual return: with a 0.03% expense ratio you end up with $173,500; with a 1% expense ratio you end up with $131,500. That $0.97/year difference per $1,000 costs you $42,000 over 30 years.

How to Invest in Index Funds 2026 — Beginner Step-by-Step Guide

Investing in index funds is straightforward: open a brokerage account, choose a low-cost index fund, set up automatic contributions, and let compound growth do the rest. Index funds are how most individual investors beat the majority of professional fund managers over time — because of lower costs, not better stock picks.

Quick answer: Open a Fidelity or Schwab account (free, no minimum), buy a total market index fund (FZROX at Fidelity or SWTSX at Schwab — both free), and set up automatic monthly contributions. That is the entire strategy for most investors.

What Is an Index Fund?

An index fund is a fund that tracks a specific market index — a predefined list of investments:

S&P 500 index: The 500 largest US publicly traded companies (Apple, Microsoft, Amazon, etc.)
Total US stock market index: All ~3,700 publicly traded US companies
Total international stock market: Companies in 40+ countries outside the US
US bond index: Thousands of US government and corporate bonds

Index funds are “passive” — they don’t require a manager making buy/sell decisions. They just hold what the index holds. This keeps costs dramatically lower than active funds.

Step-by-Step: How to Invest in Index Funds

Step 1: Choose Where to Open Your Account

The best account type depends on your goal:

Account Type	Tax Benefit	Best For
401(k) through employer	Pre-tax contributions; tax-deferred growth	Employees with employer match
Roth IRA	Tax-free growth; tax-free withdrawals	Anyone with earned income under $165K (single)
Traditional IRA	Pre-tax contributions (if eligible)	Reducing current-year taxable income
Taxable brokerage	No tax benefit, but no restrictions	After maxing tax-advantaged accounts

Open a Roth IRA first if you’re eligible — tax-free growth is powerful for long-term wealth. The 2026 contribution limit is $7,000 ($8,000 if age 50+).

Step 2: Choose a Brokerage

The best brokers for index fund investing:

Broker	Why Choose It	Best Index Funds Offered
Fidelity	No minimums; 0.00% expense ratio funds	FZROX (total market), FZILX (international), FNILX (S&P 500 equivalent)
Vanguard	Index fund pioneer; lowest costs	VOO (S&P 500), VTI (total market), VXUS (international)
Charles Schwab	No minimums; 0.03% expense ratio funds	SWTSX (total market), SCHX (large cap)

All three are excellent. Fidelity has the edge for beginners: $0 minimum, $0 commissions, and 0.00% expense ratio funds.

Step 3: Choose Your Index Fund(s)

A simple 3-fund portfolio covers everything:

US stocks — FZROX (Fidelity) or VTI (Vanguard) or SWTSX (Schwab)
International stocks — FZILX (Fidelity) or VXUS (Vanguard)
Bonds — FXNAX (Fidelity) or BND (Vanguard)

Simplest option for beginners: A single total market index fund (FZROX or VTI) covers thousands of US companies in one investment.

Step 4: Decide How Much to Invest

Any amount works. Practical starting points:

$50/month: Great start; builds habit of investing
$200/month: Grows to ~$47,000 in 10 years at 8% average return
$500/month: Grows to ~$117,000 in 10 years at 8% average return
Maximum IRA ($583/month): Grows to ~$136,000 in 10 years; maximizes tax benefits

Worked example: $300/month into FZROX (0.00% expense ratio) starting at age 30, assuming 10% average annual return, grows to approximately $1.97 million by age 65 — from $126,000 in total contributions.

Step 5: Set Up Automatic Investments

Use automatic investing to remove emotion and decision fatigue:

At Fidelity: Accounts → Select fund → Automatic investments → Set monthly amount and date
At Vanguard: Accounts → Buy → Automatic purchases → Set schedule
At Schwab: Accounts → Automatic investing → Fund → Schedule

Dollar-cost averaging (investing the same amount regularly regardless of price) has been shown to reduce the risk of investing a large lump sum at a market peak.

Key Index Fund Metrics to Compare

Metric	What to Look For
Expense ratio	As close to 0% as possible; avoid anything above 0.20%
Index tracked	S&P 500 or total market covers most investors’ needs
Number of holdings	More holdings = more diversification
Fund size (AUM)	Larger funds are more liquid and less likely to close
Tracking error	How closely the fund matches its index; lower is better

Best Index Funds for 2026

Fund	Type	Index Tracked	Expense Ratio
FZROX	Mutual fund	Fidelity Zero Total Market	0.00%
FNILX	Mutual fund	Fidelity Zero Large Cap	0.00%
VTI	ETF	CRSP US Total Market	0.03%
VOO	ETF	S&P 500	0.03%
VXUS	ETF	Total International	0.07%
SWTSX	Mutual fund	US Total Market	0.03%
IVV	ETF	S&P 500	0.03%
BND	ETF	US Aggregate Bond	0.03%

Index Funds vs. Active Funds: Why It Matters

According to SPIVA (S&P Dow Jones Indices vs. Active), over 90% of actively managed US equity funds underperform their benchmark index over 20 years, after fees. The primary reason: active funds charge 0.5–1.5% in annual fees, which compounds to a massive drag on returns over decades.

$100,000 over 30 years at 10% gross return:

0.00% expense ratio (FZROX): $1,744,940
0.50% expense ratio (typical active fund): $1,467,853
1.00% expense ratio (high-cost active fund): $1,232,459

Switching from a 1% fund to a 0.03% fund is worth $512,000 over 30 years on $100,000 invested.

Tax Efficiency of Index Funds

Index funds are highly tax-efficient for taxable brokerage accounts:

Low turnover means fewer taxable capital gains distributions
ETF structure allows in-kind redemptions, avoiding taxable events
Long-term capital gains rates (0%, 15%, or 20%) apply if held 1+ years

Written by WealthVieu

WealthVieu researches and writes data-driven personal finance guides using primary sources including the IRS, Bureau of Labor Statistics, Federal Reserve, and Census Bureau.

The content on Wealthvieu is for informational purposes only and should not be considered financial, tax, or investment advice. Consult a qualified professional before making financial decisions. Full disclaimer · Editorial policy