Wealthy PotFNILX vs FXAIX: Two Nearly Identical Fidelity Large-Cap Funds
FNILX and FXAIX are both Fidelity large-cap index funds that hold roughly the 500 biggest U.S. companies, and in practice they perform almost identically. So the choice comes down to just two things: a rounding-error fee difference, and one structural catch about ever leaving Fidelity. This guide uses figures straight from Fidelity's own fund pages.
The Short Answer
- Investing in a Fidelity IRA and want to pay literally nothing? FNILX. It charges 0.00% and holds ~509 large-cap stocks, essentially the same exposure as the S&P 500.
- Investing in a taxable account, or want the actual S&P 500 and the freedom to move brokers? FXAIX. Its 0.015% fee is a rounding error ($1.50 a year per $10,000), it tracks the real S&P 500, and unlike FNILX it can be transferred to another broker in-kind.
Their holdings are nearly the same; the decision is about the index provider and portability, not performance.
Just How Similar Are They?
Both funds own the largest U.S. companies by market value, about 500 of them, weighted by size. The difference is which index defines that list:
- FXAIX tracks the S&P 500, a committee-selected index with profitability and liquidity screens.
- FNILX tracks the Fidelity U.S. Large Cap Index, Fidelity's own proprietary index of the largest U.S. companies by float-adjusted market cap, with no committee.
In practice the two lists overlap almost entirely, so returns track within a hair of each other. FNILX can occasionally differ slightly because it adds or drops names purely by size, without the S&P committee's judgment, but the effect on returns has been minimal.
FNILX vs FXAIX Side by Side
| Feature | FNILX | FXAIX |
|---|---|---|
| Fund | Fidelity ZERO Large Cap Index | Fidelity 500 Index |
| Expense ratio | 0.00% | 0.015% |
| Index tracked | Fidelity U.S. Large Cap (proprietary) | S&P 500 |
| What it covers | ~500 largest U.S. companies | S&P 500 (large-cap U.S.) |
| Number of holdings | ~509 | ~508 |
| Minimum investment | $0 | $0 |
| Inception | Sep 13, 2018 | Feb 17, 1988 |
| Avg annual return (NAV) | 14.79% since inception (2018) | 15.49% over 10 years |
| Transfer to another broker in-kind? | No | Yes |
The return rows cover different periods (FNILX has only existed since 2018), so they are not a head-to-head race. Over any shared window the two have tracked extremely closely, as you'd expect from near-identical portfolios.
The Two Differences That Matter
1. The fee is a non-issue. FNILX is 0.00% and FXAIX is 0.015%, a difference of $1.50 per year on $10,000. Over decades this is immaterial to your outcome.
2. Portability is the real difference. FNILX, as a Fidelity ZERO fund, uses a proprietary index and is only available at Fidelity; per Fidelity's prospectus it cannot be transferred in-kind to another broker. If you ever leave Fidelity you must sell it, which can trigger capital-gains tax in a taxable account. FXAIX tracks the standard S&P 500 and moves to another broker without selling.
Rule of thumb: in an IRA, lock-in barely matters (selling triggers no tax), so FNILX's 0.00% is a fine pick. In a taxable account, FXAIX's portability is worth more than the tiny fee saving.
Which One Fits You
Choose FNILX if: you're in a Fidelity IRA, want to pay 0.00%, and are comfortable holding a Fidelity-only proprietary-index fund. The exposure is effectively the S&P 500 for free.
Choose FXAIX if: you're in a taxable account, want the actual S&P 500 benchmark, or want the option to move brokers later without a taxable sale. The fee is negligible and you gain portability and a decades-long track record. Prefer an ETF? See FXAIX vs VOO. Want the whole market instead of just large caps? See FZROX vs FXAIX.
FAQ
Is FNILX the same as FXAIX?
Nearly. Both hold roughly the 500 largest U.S. companies and perform almost identically. FNILX tracks Fidelity's proprietary large-cap index at 0.00%; FXAIX tracks the actual S&P 500 at 0.015%. The practical differences are the index provider and that FNILX can't be transferred out of Fidelity.
Is FNILX or FXAIX better?
For a Fidelity IRA, FNILX's 0.00% fee makes it a great choice. For a taxable account or if you want the real S&P 500 and broker portability, FXAIX is better despite its tiny 0.015% fee. Performance is effectively the same.
Why isn't FNILX called an S&P 500 fund?
Because it doesn't license the S&P 500 index, it uses Fidelity's own U.S. Large Cap Index to avoid licensing costs (that's how it charges 0.00%). The holdings are nearly the same large-cap companies, but the index and its rules are Fidelity's, not S&P's.
Can I move FNILX to Vanguard or Schwab?
Not in-kind. FNILX is a Fidelity ZERO fund and is only available at Fidelity; to move brokers you'd have to sell it first, which can create a taxable event in a brokerage account. FXAIX can be transferred in-kind.
Related comparisons: FZROX vs FXAIX · FXAIX vs VOO · SWPPX vs VOO · All ETF comparisons
Primary sources: expense ratios, indexes, holdings, and returns are from Fidelity's official fund pages for FNILX and FXAIX (FXAIX figures per its Jun 30, 2026 fact sheet; ZERO-fund fees as of Dec 30, 2025). The in-kind transfer restriction on Fidelity ZERO funds is per Fidelity's fund prospectus. For background, see the SEC's Investor.gov guide to mutual funds and ETFs.
This article is for educational purposes only and is not investment advice. Investing involves risk, including possible loss of principal, and past performance does not guarantee future results. Expense ratios and fund holdings change over time; confirm current figures on Fidelity's site before investing. Consult a qualified financial professional before making investment decisions.
