ETF Overlap: How to Check a Whole Portfolio

ETF overlap is the share of one fund’s holdings that another fund also holds. For a whole portfolio, the useful version is look-through exposure. List every fund’s holdings and weights. Multiply each weight by that fund’s share of your money. Add any stocks you own directly, then sum by company. The total for each stock is how much of your portfolio really rides on it. Most overlap tools compare two funds at a time and leave out your individual stocks. Those stocks are where concentration hides.

Why two-fund checks are not enough

A two-fund comparison answers one question: how much do these two hold in common? Checking the overlap between two ETFs works through that case. A real portfolio rarely stops at two. A broad market fund, a large-cap growth fund, a technology sector fund and a dividend fund can all hold the same handful of the market’s largest companies, each at a different weight, and if you also bought one of those companies directly because you like it, the same stock now reaches you through five doors.

No two-fund check adds those up. You have to.

Overlap by count and overlap by weight

Overlap checkers report two different numbers, and they can disagree badly. Count overlap is the number of holdings two funds share, divided by the number in one of them. Weight overlap adds up, for each shared stock, the smaller of its two weights. The weight version is the one that describes your money.

A count of 4% sounds like two quite different funds, yet by weight nearly a fifth of each fund is the same two companies, which is exactly the kind of overlap that shows up in your results. When a tool reports overlap, check which of the two it means before reading anything into the figure.

Gather the holdings

Each fund publishes its holdings. The fund’s own website usually has a full list with weights, often as a downloadable file, and the ETF fact sheet shows the top holdings and the date they were last updated. Use the full list where you can. Top-ten lists hide the long tail. For a concentrated fund that matters little. For a broad fund it can leave out most of the holdings.

Note the date on each file. Funds update holdings on different schedules. Compare lists from the same week if you can.

Then write down what you own:

• Each fund and its current market value.
• Each individual stock and its current market value.
• The portfolio total.

Take all of these values on the same day, so the shares you calculate later add up to exactly 100% of the portfolio.

Turn fund weights into portfolio weights

A fund weight is a share of the fund. You need a share of your portfolio. Multiply the two.

The owner of that portfolio might describe it as three diversified funds plus one stock. Almost a sixth of it moves with a single company.

Run the same multiplication for every holding in every fund. A spreadsheet handles it well: one row per fund holding, columns for fund, company, fund weight, fund share of portfolio and the product, then a pivot or a sum by company. Sort the result from largest to smallest. The top ten rows are the ones to read.

Do the same by sector

Company totals catch single-stock concentration. Sector totals catch the broader version. Most fund files include a sector for each holding, so the same sheet can sum by sector instead of by company.

Compare the result with what you meant to own. If the plan was a broad market portfolio with a tilt toward dividends, a sector split that looks like a technology fund is a sign the funds overlap more than their names suggest. Fund names describe a strategy. The holdings are what you own.

The part most checks miss

Two things slip past almost every overlap check.

The first is direct holdings. Overlap tools compare funds with funds. A stock you bought outright sits outside that comparison, and because it is usually a company you like, it is often one the funds already hold at a heavy weight. Put it in the sheet with a fund weight of 100% and its own share of the portfolio.

The second is drift. Weights move with prices. A stock that rises faster than the rest of the market grows inside every fund that holds it, and it grows in your direct holding too, so the look-through total can climb for months without any trade, and a portfolio you checked once at the start can be far more concentrated now than the day you built it.

That is before the funds’ own weights in Company X rise with it. Recheck after any large move in your biggest holdings.

What to do with the result

Decide on a ceiling first. Pick the largest share of the portfolio you would accept in one company and in one sector, write both numbers down before you look at the sheet, and only then compare them with the totals.

If a company is over the ceiling, you have a few choices. Trim the direct holding, since it is usually the easiest piece to change. Replace one of the overlapping funds with one that holds less of the same names. Or accept the concentration knowingly and write down why. Each is a fair answer. Holding it by accident is the only poor one.

Track the effect over time as well. Calculating portfolio returns shows how to measure the whole portfolio’s result with cash flows included, which tells you whether the concentration has helped or hurt.

Where overlap is fine

Overlap is not always a problem. A core broad market fund plus a small satellite fund will overlap heavily by design, and the point of the satellite is the tilt it adds at the margin. Overlap only becomes a problem when it is bigger than you thought, or when it concentrates risk you never meant to take.

What goes wrong

• Comparing funds two at a time and never adding them up.
• Using top-ten holdings for a broad fund.
• Leaving individual stocks out of the sheet.
• Mixing holdings files from different months.
• Checking once and never again.