FNILX vs FXAIX is a fight over $1.50. FNILX (Fidelity ZERO Large Cap Index) charges a 0.00% expense ratio, while FXAIX (Fidelity 500 Index) charges 0.015%, which is $1.50 a year on $10,000. The bigger difference is the index each one follows, and that matters more than the fee.
Neither side of FNILX vs FXAIX is a bad choice. Both hold roughly 500 large U.S. companies, both have no minimum, and both are run by Fidelity. This guide shows the 2026 numbers, the cost in real dollars and who should pick which.
This is general information, not personalized financial advice. Check current fund details at Fidelity before you invest.
Quick Facts
| Feature | FNILX | FXAIX |
|---|---|---|
| Full name | Fidelity ZERO Large Cap Index Fund | Fidelity 500 Index Fund |
| Expense ratio | 0.00% | 0.015% |
| Index followed | Fidelity U.S. Large Cap Index | S&P 500 |
| Holdings | About 508 | 508 (Aug 31, 2026) |
| Net assets | About $19.4 billion | About $857.6 billion (Sept 30, 2026) |
| Inception | September 13, 2018 | February 17, 1988 |
| Minimum investment | $0 | $0 |
| Where you can buy it | Fidelity brokerage accounts | Fidelity, plus some other brokers |
| Fund type | Mutual fund | Mutual fund |
FXAIX data comes from Fidelity’s fund fact sheet. FNILX asset and holdings figures come from AAII’s fund summary and carry no stated date, so treat them as approximate.
What Is FNILX vs FXAIX?
FNILX vs FXAIX is the matchup between Fidelity’s two large-cap U.S. stock index mutual funds. FNILX is the zero-fee fund, and FXAIX is the longtime S&P 500 fund.
In the FNILX vs FXAIX debate, both are passive funds, meaning they try to copy an index instead of picking stocks. Both are sold by one company, so the FNILX vs FXAIX question isn’t which firm to trust. It’s which index and which fee you’d rather own.
Why does it matter? Over decades, small differences compound. A fund that charges less can win, but only if it also tracks a similar index.
How These Funds Work
To understand FNILX vs FXAIX, start with the basics. An index fund buys the stocks in a benchmark in roughly the same proportions. When the benchmark changes, the fund trades to match it. Fees come out of the fund’s returns, so a lower expense ratio leaves more of the return with you.
FXAIX follows the S&P 500, which is chosen by a committee at S&P Dow Jones Indices. Companies must meet size, liquidity and profitability rules to be added. FNILX follows Fidelity’s own U.S. Large Cap Index, which uses its own rules.
Fidelity says FNILX is one of four ZERO expense ratio index funds, and that it’s “available to individual retail investors who purchase their shares through a Fidelity brokerage account,” according to its index funds overview. That last detail is easy to miss and becomes important later.
FNILX vs FXAIX: Head-to-Head
Cost
FNILX’s fee is 0.00%, and FXAIX’s is 0.015%, as of Fidelity’s April 2026 data. That’s a gap of $1.50 a year per $10,000.
At $100,000, the gap is $15 a year. At $500,000, it’s $75. That’s real money, but small compared with market swings of thousands of dollars in a single month.
The index
This is the main difference. The S&P 500 includes companies that meet specific rules, including a profitability requirement. Fidelity’s index is built by market size without that screen, according to Retire Before Dad, so FNILX can hold large companies that the S&P hasn’t yet admitted.
In practice, the two portfolios overlap heavily, and estimates run from about 95% to 99%. That means most of your money buys the same stocks either way.
Holdings and concentration
Both funds hold about 508 securities, but they’re top-heavy. FXAIX’s top 10 holdings made up roughly 39% of the fund on August 31, 2026, led by Nvidia (8.08%), Apple (7.03%) and Microsoft (5.69%). AAII shows FNILX’s top 10 at 36.9%.
If you hold either fund, you hold a lot of a handful of big tech names. That’s the S&P 500’s structure, not a flaw in the fund.
Size and track record
FXAIX has been around since 1988 and holds about $857.6 billion, while FNILX launched in 2018 and holds around $19.4 billion. Both are large and liquid enough that size isn’t a practical concern.
In FNILX vs FXAIX, the track record is the real difference. FXAIX has more than 35 years of history, while FNILX has fewer than eight.
Where you can hold it
This is the catch. FNILX is sold through Fidelity brokerage accounts. If you later move to another broker, you may not be able to transfer the shares as they are, and selling in a taxable account could trigger capital gains. That consequence is our inference from Fidelity’s availability rule, so confirm the details with Fidelity before moving.
FXAIX is easier to move, including to some other brokers, though some charge fees, so check yours.
FNILX vs FXAIX in 2026: Performance
As of September 30, 2026, FXAIX’s annualized returns were 15.72% over one year, 22.87% over three years, 13.78% over five years and 15.32% over 10 years, according to Fidelity’s fact sheet.
AAII lists FNILX at about 15.3% over one year, 23.0% over three years and 13.5% over five years, but it doesn’t state the date, so we can’t compare the two directly. Past returns don’t predict future results.
BrokerChooser offers a cleaner comparison. As of August 6, 2026, it showed FNILX trailing Vanguard’s VOO (also an S&P 500 fund) by 0.45 percentage points over one year and by 2.29 points cumulatively over five years. That works out to roughly a quarter of a percentage point a year, which is our own rough conversion.
That gap is bigger than the 0.03% fee VOO charges, and bigger than the 0.015% FXAIX charges. In other words, the index can matter more than the fee. But gaps like this swing in either direction over time, so treat it as a useful warning and not a verdict.
What the Fee Actually Saves You
Here’s an illustration of the fee gap. These figures assume a 7% annual return before fees, which is an assumption and not a forecast:
| Scenario | Fee savings with FNILX over FXAIX |
|---|---|
| $10,000 lump sum, 30 years | About $342 |
| $100,000 lump sum, 30 years | About $3,418 |
| $500 a month for 30 years | About $1,726 |
Those are real savings, but compare them with the return gap above. A quarter of a point per year would wipe them out, and a tracking gap in the other direction would add to them.
The takeaway from FNILX vs FXAIX: the fee gap is a rounding error next to your savings rate, your time in the market and whether you stay invested during a downturn.
Comparison: FNILX, FXAIX and Alternatives
| Fund | Expense ratio | Index | Best for |
|---|---|---|---|
| FNILX | 0.00% | Fidelity U.S. Large Cap | Fidelity-only investors |
| FXAIX | 0.015% | S&P 500 | Tracking the classic benchmark |
| FSKAX | 0.015% | Dow Jones U.S. Total Stock Market | Broader exposure to small and mid caps |
| VOO | 0.03% | S&P 500 | Investors outside Fidelity |
| FZROX | 0.00% | Fidelity U.S. Total Market | Zero-fee total market at Fidelity |
If you’re deciding between large-cap and total-market exposure, our guide on FSKAX vs FXAIX explains how adding small and mid-size stocks changes the picture. FZROX’s details come from Fidelity’s ZERO fund lineup, so confirm its current fee at Fidelity.
How to Decide on FNILX vs FXAIX in Four Questions
Instead of comparing every statistic, answer four questions. Your answers usually settle the FNILX vs FXAIX choice in a few minutes.
Will I stay at Fidelity? If yes, FNILX’s availability limit won’t matter to you. If you might move your accounts someday, FXAIX is easier to take with you.
Do I want the S&P 500 specifically? Many investors want the benchmark itself, partly because it’s the standard that every other fund is measured against. If that matters, FXAIX is the direct choice.
Is this a taxable account? In a taxable account, an unnecessary sale creates a tax bill. Pick the fund you’re comfortable holding for years, since switching in the FNILX vs FXAIX contest can cost more than the fee you save.
Do I care about a few dollars a year? If the answer is yes, FNILX saves them. If you’d trade that for a longer track record, FXAIX wins. Either answer is reasonable.
Practical Takeaways
Choose FNILX if you plan to stay at Fidelity for the long haul, want the lowest possible fee and are comfortable with a newer fund and a different index.
Choose FXAIX if you want the S&P 500 itself, a long track record or the flexibility to move brokers more easily.
Hold both if you can’t decide. They overlap heavily, so it won’t diversify much, but it also won’t hurt. Just don’t pay taxes to switch from one to the other in a taxable account over a $1.50 difference.
Think about the account, too. Inside an IRA or 401(k), switching has no tax cost, so the choice is easier. In a taxable account, picking once and sticking with it matters more than picking perfectly.
Finally, don’t let this decision overshadow bigger ones. Whether you invest all at once or over time matters more, and our breakdown of dollar-cost averaging vs lump sum with $10,000 walks through that trade-off. And before you put money into anything, be wary of products like those covered in IUL vs 401(k), where the real cost is hidden in fees.
For more on index funds and long-term investing, browse our Investing guides.
People Also Ask
What is the difference in FNILX vs FXAIX?
FNILX is Fidelity’s zero-fee large-cap fund that tracks Fidelity’s own index, while FXAIX charges 0.015% and tracks the S&P 500.
Is FNILX better than FXAIX?
In FNILX vs FXAIX, neither is clearly better. FNILX is cheaper, but FXAIX tracks the S&P 500 and has a far longer track record.
Does FNILX track the S&P 500?
No. It tracks Fidelity’s U.S. Large Cap Index, which holds similar stocks but uses different rules.
Is a 0.00% expense ratio really free?
The fund doesn’t charge a management fee, but returns can still differ from an S&P 500 fund because of the index, so the true cost isn’t always zero.
Can I hold FNILX outside Fidelity?
Fidelity says it’s available to retail investors through Fidelity brokerage accounts, so moving brokers may require selling.
Which is better for a Roth IRA?
Either works. Inside a Roth IRA there are no tax costs on trades, so the choice comes down to index preference and fee.
How much does 0.015% cost per year?
It costs $1.50 a year per $10,000 invested, or $15 per $100,000.
Does FNILX have a minimum investment?
No. Both FNILX and FXAIX have no minimum at Fidelity.
Is FNILX riskier than FXAIX?
They hold similar large U.S. companies, so risk is very similar. Both can fall sharply in a bear market.
Can I own both?
Yes, but they overlap by an estimated 95% to 99%, so owning both adds little diversification.
How big is FXAIX?
About $857.6 billion in net assets as of September 30, 2026, according to Fidelity.
Who is winning FNILX vs FXAIX on performance?
Over the last five years, FNILX has trailed an S&P 500 fund by roughly a quarter point per year, per BrokerChooser’s August 2026 figures, but the gap can reverse.
The Bottom Line
FNILX vs FXAIX is a close call. FNILX saves you $1.50 per $10,000 each year, while FXAIX gives you the S&P 500, a 35-year record and easier portability. The index difference has mattered more than the fee over the past five years.
Pick the one that fits your account and your plans, avoid selling one to buy the other in a taxable account, and keep investing regularly. For more practical money guides, visit Snoopstats.
