RSP vs VOO: Same 500 Stocks, Half the Overlap

Disclaimer: This content is not investment advice. Investing involves the risk of loss of principal. Past performance does not guarantee future results. Always consult a qualified financial advisor before making investment decisions.

If two funds hold the same 500 companies, they must be nearly identical — that is the intuition, and it is wrong. The Invesco S&P 500 Equal Weight ETF (RSP) and the Vanguard S&P 500 ETF (VOO) draw from the same index, share 502 positions, and still register a weighted overlap of only 46.49% — a Moderate Overlap verdict on the live RSP vs VOO comparison.

That gap between "same holdings" and "same exposure" is the single most useful thing to understand about ETF overlap.

Why the Same Stocks Produce Different Portfolios

VOO weights each company by market capitalization. The largest company gets the largest slice, and the effect compounds: the top ten positions alone can account for a third or more of the fund.

RSP holds the identical roster but assigns every company roughly the same weight, rebalancing quarterly. A $4 trillion megacap and a $20 billion mid-cap each get about 0.2%.

So the rosters match almost perfectly while the dollars land in very different places. Overlap measures dollars.

What the Weighted Formula Actually Counts

The overlap score sums, for each shared holding, the smaller of its two weights:

Overlap = Σ min(weight in Fund A, weight in Fund B)

Consider a megacap held at 7% in VOO and 0.2% in RSP. It contributes just 0.2% to the overlap score, not 7%. The other 6.8% of VOO's position has no counterpart in RSP — it is exactly the concentration that RSP was built to avoid.

Repeat that across the largest fifty companies and the arithmetic becomes clear. The two funds agree on which companies to own and disagree sharply on how much of each to own, so roughly half the weight fails to pair up.

The Practical Consequence

Holding RSP alongside VOO is one of the few "both funds, same index" pairings that genuinely changes a portfolio's shape rather than merely duplicating it:

• Concentration. VOO's return is driven disproportionately by its largest names. RSP's is not.
• Sector drift. Cap weighting lets whichever sector is winning grow into a larger share over time. Equal weighting resets that drift at each rebalance.
• Size tilt. Equal weighting effectively tilts toward the smaller members of a large-cap index.
• Cost and turnover. RSP's quarterly rebalance carries higher turnover and a higher expense ratio than VOO's near-zero fee.

None of that makes one fund better. It makes them genuinely different exposures, which is precisely what a Moderate Overlap score is telling you.

Compare This to a Real Duplicate

The contrast is sharpest against two funds tracking the same index the same way. VOO vs IVV scores 97.16% — both cap-weight the S&P 500, so nearly every dollar pairs up. Same index, same method, near-total duplication.

Same index, different method, and the overlap falls by half. Method is the variable that matters.

How to Apply This

When you are deciding whether a second fund earns its place, do not stop at "how many holdings do they share?" Ask what fraction of the weight is duplicated:

1. Open the pair on the overlap checker and read the weighted score, not the shared-holdings count.
2. Look at the top shared holdings table. If the largest positions contribute far less overlap than their headline weights suggest, the two funds weight them very differently.
3. Decide whether the non-overlapping portion is exposure you actually want.

For the mechanics behind the score, see the ETF comparison methodology guide. For a portfolio-wide pass, see how to reduce ETF portfolio overlap.

Conclusion

RSP and VOO are the cleanest demonstration that shared-holding counts are a poor proxy for duplicated exposure. 502 shared positions, 46.49% shared weight. The roster is the same; the portfolio is not.

Check any pair you own at ETF Overlap Checker — free, no account required.