FILE / VOO-VFIAX
2026 edition
VANGUARD S&P 500 PAIR / SEC CIK 0000036405
VOO vs VFIAX: dual share classes, single underlying fund
Both are Vanguard's S&P 500 fund, filed under SEC CIK 0000036405 (Vanguard Index Funds). Same portfolio, same manager, same dividends. The choice between them is mechanical, governed by SEC Rule 6c-11 for the ETF class and 1940 Act § 22(d) for the mutual fund class.
LIVE SEC DATA / FIG. 0
From the most recent N-CSR filing on EDGAR
Both share classes file together under CIK 0000036405. The numbers below come from the same set of SEC filings; the only thing that changes between rows is which share class the issuer is reporting on.
QUICK VERDICT
read this if nothing elsePick the ETF if
You are at a broker other than the home brokerage, starting under $3,000, want intraday pricing, or want maximum tax efficiency in a taxable account.
Pick the index fund if
You are already at the home brokerage, have $3,000 to start, and want clean automatic monthly investing into a single ticker.
Performance over any reasonable holding period is effectively identical because the two share classes are claims on a single underlying portfolio (CIK 0000036405). The dual share-class structure operated under US Patent 6,879,964 (issued 12 April 2005, expired 16 May 2023), giving VFIAX unusually good tax efficiency for a mutual fund because the ETF class's in-kind redemption mechanism under Rule 6c-11(c)(2) and 26 U.S.C. § 852(b)(6) sweeps low-basis stock out for both classes. Outside this structure, the ETF wrapper still has the structural tax-efficiency edge.
Expense ratios, AUM, and yield in the table above come from each share class's most recent N-CSR filing under SEC EDGAR CIK 0000036405. The issuer's product pages are derived from these same SEC filings under Rule 482 of the 1933 Act. Confirm the current prospectus (Form 485BPOS) before acting; we refresh monthly.
FIG. A / SPEC SHEET
Side by side
When to pick VOO
- You are at Fidelity, Schwab, Robinhood, or any broker outside the home brokerage.
- You are starting with less than $3,000 (the VFIAX Admiral minimum).
- You want to tax-loss harvest or execute a lump sum at a known price.
- You hold in a taxable brokerage account and want maximum tax efficiency.
- You prefer being able to see a live price and place limit orders.
When to pick VFIAX
- You are at the home brokerage with at least $3,000 to start.
- You want to set up a recurring monthly contribution and forget about it.
- You hold in a Roth IRA or Traditional IRA where tax efficiency does not matter.
- You want exact dollar investing (e.g. $537 per month, not "buy 1 share plus leftover cash").
- You prefer not to see live price ticks. Less temptation to fiddle.
FIG. B / STRUCTURAL NOTE
Why VFIAX is unusually tax-efficient (for a mutual fund)
The issuer held US Patent 6,879,964, originally filed 9 March 2001, issued 12 April 2005, expired 16 May 2023. The patent covered a method of operating a single regulated investment company that issues both mutual fund shares and ETF shares as separate classes. The ETF share class performs in-kind redemptions under 26 U.S.C. § 852(b)(6) and SEC Rule 6c-11(c)(2) on behalf of the entire fund, absorbing low-basis stock and sweeping away embedded gains that would otherwise be passed through to the mutual fund's holders as § 852(b)(3) capital gain dividends. Per the most recent N-CSR filings on EDGAR under CIK 0000036405, VFIAX has historically distributed far fewer capital gains than peer index mutual funds.
Now that the patent has expired, other issuers can in principle build similar structures. Multiple firms have filed exemptive-relief applications under Section 6(c) of the 1940 Act through SEC EDGAR. For now, the practical takeaway: VFIAX in a taxable account is roughly as tax-efficient as VOO. Outside the existing dual-class trust structures, that equivalence does not hold.
DESK Q&A
Frequently asked
Q01Do VOO and VFIAX hold exactly the same stocks?
Yes. Both share the same S&P 500 portfolio under CIK 0000036405. The dual share-class structure means the ETF wrapper and the mutual fund wrapper are claims on the same underlying holdings, run by the same team. The fund's Form N-PORT (monthly portfolio holdings) confirms the holdings are pooled at the fund level, not segregated by share class. Tracking differences over time come from minor cash-management lags and the 1 bp expense ratio differential, not from different investment decisions.
Q02If I have $3,000 and a Roth IRA at the home brokerage, which is better?
VFIAX is the slightly cleaner choice for that scenario. The 26 U.S.C. § 852(b)(6) tax efficiency of the ETF wrapper is irrelevant inside a Roth IRA (qualified distributions are tax-free under 26 U.S.C. § 408A(d)). The mutual fund interface lets you set a recurring contribution amount in dollars, no need to think about share prices or fractional support. VOO would also work fine, just with marginally more friction.
Q03Can I convert VFIAX to VOO without selling?
Yes. The issuer supports a tax-free conversion from the mutual fund share class to the ETF share class within a taxable account at the home brokerage. Because both classes are claims on the same underlying fund (CIK 0000036405), the conversion is treated as an exchange between share classes of the same RIC and does not trigger gain recognition under the share-class regulations under Sections 851 and 852 of the IRC. The reverse (ETF to mutual fund) is not supported. This is one reason some investors who plan to hold long-term in a taxable account start with VFIAX (for the auto-invest convenience) and convert to VOO later.
Q04Does the bid-ask spread on VOO meaningfully cost me money?
Not for buy-and-hold. SEC Rule 6c-11(c)(3)(D) (17 CFR 270.6c-11(c)(3)(D)) requires the issuer to publish the prior-business-day median bid-ask spread; VOO's typically runs in the $0.01 range. On a $5,000 purchase that is roughly $0.10 of round-trip cost. Negligible compared to expense ratios, taxes, and contribution rate. Verify the live figure on the issuer's product page or via the FINRA Fund Analyzer.
Q05Has VOO outperformed VFIAX historically?
Within tracking error, no. The annualised difference over 10-year windows is typically less than 0.05 percentage points and can run either direction depending on cash drag, distribution timing, and the 1 bp expense-ratio gap reported in each share class's annual N-CSR. For practical retail investing, treat the two as identical.
Q06Where do I see VOO's most recent SEC filing?
Go to SEC EDGAR (sec.gov/edgar/searchedgar/companysearch), search by CIK 0000036405, and filter by N-CSR for the semi-annual report or 485BPOS for the annual prospectus amendment. The most recent N-CSR contains audited financial statements, schedule of investments, and the expense ratio reconciliation; the 485BPOS contains the currently effective prospectus.
DESK ROUTING