---
title: "Measuring ETF overlap: holdings, weights and look-through"
description: "Measure ETF overlap correctly: shared holdings, weighted overlap and portfolio look-through. Includes formulas and a transparent worked example."
canonical: "https://investboard.com/knowledge/etf-overlap"
language: "en"
published: "2026-03-27"
modified: "2026-09-05"
last_verified: "2026-09-05"
author: "David Bartas"
author_url: "https://investboard.com/about"
reviewer: "David Bartas"
reviewed: "2026-07-27"
---

# Measuring ETF overlap: holdings, weights and look-through

MSCI World and S&P 500: why shared holdings, weighted overlap and portfolio exposure answer different questions.

## In short

ETF overlap needs a clearly defined measure. Counting shared holdings describes the intersection; weighted overlap sums the smaller fund weight for each holding. ETF look-through also scales holdings by your portfolio allocation. A rate without fund names, a holdings date and data coverage cannot be interpreted reliably. Deliberate overlaps should fit the concentration limits in your investment mandate.

- Shared holdings, weighted overlap and portfolio exposure are different measures.
- Weighted overlap sums the smaller fund weight for each holding.
- ETF look-through also accounts for your own portfolio weights.
- A sound rate requires complete dated holdings and disclosed data gaps.

Two ETFs can hold the same companies. Whether that creates an unwanted concentration depends on the weights in your whole portfolio. ETF look-through makes those weights visible.

## MSCI World and S&P 500: What overlaps

MSCI World includes large and mid-cap companies from developed markets, including the United States. The S&P 500 tracks large US companies. Combining them does not simply add a new market: many US holdings appear in both. See the [MSCI index overview](https://www.msci.com/indexes/index/990100) and the [S&P Dow Jones Indices overview](https://www.spglobal.com/spdji/en/indices/equity/sp-500/).

A blanket claim such as “70 percent overlap” is uninformative without a method and date. The US share of index weight is neither the proportion of shared holdings nor the weighted overlap between two funds. A country's weight and a company's domicile also do not tell you where its revenues originate.

This article does not report a current overlap rate for MSCI World and the S&P 500. That requires complete holdings for two specifically identified funds on the same date. The calculation below is entirely illustrative, not a measurement of those indices.

## Three measures, three different questions

### Count shared holdings

How many securities appear in both funds? State the intersection and the denominator: shared holdings divided by all holdings in fund A. The equivalent proportion for fund B can differ. A measure based on the union of all holdings would be different again.

### Measure weighted overlap

How similar are the fund weights? For each shared holding, take the smaller of its two fund weights and add those values. With weights between 0 and 1, the sum lies between 0 and 1. Two identical, fully covered portfolios yield 100 percent; no shared holdings yield 0 percent.

### Weighted overlap

```text
Overlap = sum across all holdings i of min(weight in fund A, weight in fund B)
```

### Look through the whole portfolio

How much of your portfolio depends on one company? Multiply each fund's portfolio weight by its weight in that company. Add the contributions from every fund and any directly held shares. This combined exposure also depends on your own allocation.

### Look-through weight

```text
Portfolio weight of company i = sum of (fund's portfolio weight × company's fund weight) + directly held portfolio weight
```

## A fully worked example

Assume two fictional, fully invested funds with three companies each. There is no cash, no derivatives and no unknown holdings. The illustrative portfolio allocates 60 percent to fund A and 40 percent to fund B.

| Company | Fund A | Fund B | In the 60/40 portfolio |
| --- | --- | --- | --- |
| Alpha | 50 % | 20 % | 38 % |
| Beta | 30 % | 50 % | 38 % |
| Gamma | 20 % | 0 % | 12 % |
| Delta | 0 % | 30 % | 12 % |

- **By count:** Alpha and Beta are shared. That is 2 out of 3 holdings in each fund, or about 66.7 percent. Relative to all 4 distinct companies it would be 50 percent.
- **By weight:** min(50 %, 20 %) + min(30 %, 50 %) = 20 % + 30 % = **50 percent overlap**.
- **In the portfolio:** Alpha weighs 60 % × 50 % + 40 % × 20 % = **38 percent**. Beta also weighs 38 percent. Together, **76 percent of the portfolio is invested in the shared companies**.

The 76 percent is not an additional loss or double-counted wealth. It is the share of the portfolio invested in companies held through both funds. It answers a different question from the 50 percent weighted overlap.

## Holdings dates and limits of look-through

A sound calculation needs the specific funds, complete dated holdings and your current portfolio weights. Match securities using stable identifiers. To compare companies rather than security lines, first combine different share classes issued by the same company.

Top-ten lists cannot establish a complete overlap rate. Missing holdings remain unknown: do not classify them as non-overlapping or silently scale known holdings to 100 percent. Report coverage separately. For synthetic ETFs, the collateral basket can differ from the economic exposure of the index. Cash and derivatives also need explicit treatment.

[Investboard's portfolio analysis](/product/analysis) places look-through in the context of the whole portfolio. A result without a holdings date and coverage level should not trigger a reshuffle.

## Compare the overlap with your mandate

A deliberate overweight is not automatically a mistake. What matters is whether it fits your target allocation and concentration limits. A single broad ETF can also be concentrated; the number of funds alone is not a risk measure.

Record intended concentrations in your [investment mandate using the IPS template](/knowledge/investment-policy-statement). If an overlap surprises you, check the data and your rules first. A [cooling-off period](/knowledge/cooling-off) creates time for this. Before changing anything, include the [cost of tinkering](/knowledge/the-quiet-cost-of-tinkering) in the assessment.

## Frequently asked questions

### How much overlap do MSCI World and the S&P 500 have?

There is no timeless rate. A reliable figure needs holdings for specifically identified funds on the same date and a defined method. MSCI World's US weight is neither the proportion of shared holdings nor the weighted overlap.

### How is weighted ETF overlap calculated?

For each shared holding, take the smaller weight from the two funds and add those values. In the illustrative example with Alpha (50 and 20 percent) and Beta (30 and 50 percent), that is 20 plus 30, or 50 percent.

### What does ETF look-through add?

It multiplies the funds' portfolio weights by their company weights and adds direct holdings. In the illustrative 60/40 portfolio, Alpha and Beta each account for 38 percent. The combined 76 percent in shared companies is not a weighted-overlap rate.

### Do I need to sell overlapping ETFs?

Overlap alone is not an instruction to sell. Check holdings dates, coverage, target allocation and concentration limits in your mandate. Before changing anything, consider costs, possible taxes and your cooling-off rule.

## Sources

- [MSCI World Index: Abdeckung und Methodik](https://www.msci.com/indexes/index/990100) · MSCI
- [S&P 500: Indexübersicht und Methodik](https://www.spglobal.com/spdji/en/indices/equity/sp-500/) · S&P Dow Jones Indices