Equal Weight vs Market Cap ETF: Same Stocks, Different Bets

Divide 100% by 500 and you get 0.2%. Every company in an equal weight S&P 500 index starts each quarter at that slice, the largest business in the country and the smallest member alike.

How does a market cap ETF decide each weight?

By size. A company’s weight in a cap-weighted index is its market value divided by the combined market value of every member, so the weight rises and falls with the share price each trading day, and the fund tracking that index ends up holding more of a stock that has climbed without anyone at the fund placing an order to buy it. Winners grow on their own. Nothing needs selling when a stock rallies.

The table sets the best-known cap-weighted S&P 500 funds beside the equal weight one. As of October 2026, the sponsors’ pages list the S&P 500 Index as the benchmark for SPY, IVV and VOO.

Fund	Ticker	Sponsor	Weighting
SPDR S&P 500 ETF Trust	SPY	State Street	Market value
iShares Core S&P 500 ETF	IVV	iShares	Market value
Vanguard S&P 500 ETF	VOO	Vanguard	Market value
Invesco S&P 500 Equal Weight ETF	RSP	Invesco	Equal, reset quarterly

Same companies in every row. Only the last row sizes them differently.

How does an equal weight ETF work?

RSP tracks the S&P 500 Equal Weight Index, which S&P Dow Jones Indices builds from the S&P 500’s own member list. As of October 2026, Invesco’s fund page says each company carries the same 0.20% weight and that the fund and its index are rebalanced quarterly.

Between those dates the weights drift. A stock that rises 40% in a quarter while another falls 20% will finish the quarter well above 0.2% while the faller sits well below it, and on the rebalancing date the index sells part of the winner and buys more of the loser to put both back at the same slice. That trade happens by rule. No one judges whether the winner has further to run.

What does a quarter of drift look like?

Take a hypothetical index holding stocks A, B, C and D. Give it $10,000 and run it through one quarter both ways.

Read the two blocks as structure. The equal weight version sold its best performer and bought its worst, which it will do again next quarter whatever the news. The cap-weighted version let its largest holding grow from 40% to nearly 48% without a single order. The dollar totals differ only because the starting weights were assumptions, and they say nothing about which method earns more over time, since that depends on whether the leaders keep leading, which no weighting rule can know in advance.

How concentrated is the cap-weighted S&P 500?

Invesco’s September 2026 insight on equal weighting, using data as at 31 August 2026, put the 10 largest S&P 500 companies at 37% of the index. In 2014 the same group held less than 20%. Weights move daily.

So 37 cents of every dollar in a cap-weighted S&P 500 fund sat in ten companies on that date. In the equal weight fund, just after a reset, it was 2 cents. Equal weighting is built to shrink that gap, and the Mag 7 investing case study runs the look-through sum on a whole portfolio of index funds and direct shares to show how much of it can end up in a handful of names.

Which sectors and sizes does each one lean toward?

Equal weighting sets a sector’s share by headcount. At a reset, a sector’s weight is simply the number of its members divided by the number of companies in the index.

A sector made of a few giants shrinks. A sector crowded with mid-sized members grows. So the sector split of RSP can look quite unlike SPY’s even though every company in one is in the other, and the gap widens whenever a small group of very large companies in one industry pulls away from the rest of the index.

Size follows the same logic. Invesco’s own description says the approach “tilts toward smaller companies in the S&P 500 Index.” The smallest member gets 0.2%, the same as the largest. Smaller companies can swing harder on a bad quarter, and that risk comes with the tilt.

To see the difference for yourself, open the sector breakdown on each fund’s page and compare them on the same date.

Is NOBL an equal weight fund too?

It is, by its own rules. ProShares’ fund profile for the ProShares S&P 500 Dividend Aristocrats ETF (NOBL), read in October 2026, describes an equal weighting methodology, a minimum of 40 stocks, a 30% ceiling on any single sector, and a quarterly return to equal weights in January, April, July and October, with the yearly membership review done at the January rebalance.

The filters stack. The dividend aristocrat streak decides who gets in. Equal weighting decides how much each member gets. The sector mix that results comes from which industries happen to hold long dividend streaks, so it bears little resemblance to RSP’s mix, even though both funds start from the S&P 500 and both hand every holding the same slice.

What does turnover cost inside the fund?

Every reset is a round of trades. The fund pays the commissions and spreads out of its assets, and that cost becomes part of the gap between the fund’s return and its index, the gap measured by tracking error and tracking difference. A cap-weighted fund trades mainly when the index adds or drops members. In a quiet quarter it places few orders.

Each fund’s prospectus and annual report give a portfolio turnover rate for the fiscal year. Put RSP’s figure next to SPY’s, IVV’s or VOO’s from the same kind of document. The equal weight fund’s rate carries its quarterly resets.

What does equal weighting cost if you do it yourself?

The arithmetic above works the same on an account you run. Twenty stocks at 5% each is an equal weight portfolio, and the how many stocks should you own guide sets out why a cap on each position matters. Keeping that cap means selling winners.

In a taxable account a sale at a profit realizes a capital gain. Use stock A from the drift example, bought for $2,500 and now worth $3,500.

Repeat that every quarter across a full list of winners and the reset produces a steady stream of small taxable gains, plus the time spent placing every order. Inside an IRA the sales carry no current tax, though every order still has to be placed.

Funds handle this inside their own structure. As of October 2026, Invesco’s RSP page states the fund has not paid a capital gains distribution since its inception in 2003. That is a record of the past, and the next year can differ, so check the fund’s distribution history before relying on it. Tax situations differ.

Which one fits your portfolio?

Pick the cap-weighted fund if you want the index as the market prices it, with almost no trading and the largest companies at full size. Pick equal weight if a 37% top-10 share is more single-company exposure than you want, and you accept the extra turnover, a different sector mix and a lean toward smaller members. Holding both is also possible.

Set the split from the top-10 number you can live with. Recheck it when the weights move.