Your Complete Guide to Index Investing with Dan Bortolotti

An ETF Creation Story

2018-06-17T21:35:59+00:00December 28th, 2011|Categories: ETFs and Funds, Indexing Basics|Tags: |12 Comments

The Couch Potato strategy thrives on simplicity, but advanced index investors (geeks) should understand what goes on under the hood of ETFs. One of the most important concepts is how ETF shares are created and redeemed. I’ll warn you that this gets a bit technical. But it turns out that this process is the single most important difference between ETFs and index mutual funds.

Let’s begin by looking at how a mutual fund creates new shares (or units). When you make a $2,000 contribution, your money goes directly to the mutual fund’s manager, who uses it to buy more securities. If the fund’s net asset value (NAV) per share is $20, the manager then creates 100 new shares ($2,000 ÷ $20) just for you. This is what’s meant by the term open-end fund: the number of units changes every time money moves in or out.

Closed-end funds, by contrast, do not create or redeem new units. They are launched with a finite number of shares, and if you want to invest in the fund you have to buy your shares from another investor who is willing to sell.

An open-ended discussion

ETFs trade on an exchange like closed-end funds, but they are open-ended: new shares are created to meet investor demand. Unlike mutual funds, however, ETFs do not create new units every time money flows in.

Instead, whenever necessary, ETF providers issue a large block of shares called a Prescribed Number of Units (PNU), typically in multiples of 50,000. The providers then work in partnership with third-party “designated brokers,” or DBs, who distribute these units to the public. A new ETF might be launched with 200,000 units, for example, and several DBs would  divide these up and sell them on the secondary market. Going forward, when invetsors want to sell their units, the DBs are obliged to buy them back at a price very close to their net asset value.

(Geeky footnote: ETF providers south of the border use different terminology. If you’re reading American books or websites, PNUs are called creation units, and designated brokers are called authorized participants. Feel free to share this fun fact with your friends and coworkers.)

When you purchase $2,000 worth of an ETF trading at $20, the DB will simply fill your order with 100 shares from its inventory. However, if an institutional investor wants to buy $2 million worth of shares, the DB will not have enough inventory. So it will credit the investor’s account for 100,000 shares and simultaneously purchase $2 million worth of the fund’s underlying holdings. Then the broker will deliver that basket of stocks or bonds to the ETF provider, who will create 100,000 new shares and send them to the DB as payment.

That wasn’t so hard, was it?

Redeeming qualities

This creation-redemption process may be complicated, but it has a couple of important benefits.

First, if the ETF is selling at a premium, a designated broker can buy the fund’s underlying securities and simultaneously sell shares of the ETF, thus making a risk-free profit. (If it is selling at a discount, the DB can do the opposite.) This presents an arbitrage opportunity, and when multiple DBs compete with each other to profit from it, the result is that the ETF’s price stays close to the NAV. That, of course, is exactly what investors want.

Second, the process prevents buy-and-hold ETF investors from being penalized by active traders. An inherent problem with mutual funds is they must always keep cash on hand to pay investors who redeem their shares, and this uninvested money is a drag on the fund’s returns. Worse, when investors sell in droves (such as during a market decline), the mutual fund has to liquidate holdings to pay them, which can mean forced sales and tax consequences for the fund’s other investors. ETFs never have to do this: if investors flee, the designated broker can just return blocks of shares to the ETF provider and receive the underlying securities in exchange. Because this is an “in-kind redemption” and not a sale, there is no taxable event.

For more information about the nuts and bolts of ETF construction, I recommend All About Exchange-Traded Funds, a new book by Scott Paul Frush (McGraw-Hill, 2011).


  1. DM December 28, 2011 at 9:55 pm

    @CCP, thanks for this technical information Dan. This is actually immensely helpful. Can pension funds and other institutional investors act as DBs?

  2. Canadian Couch Potato December 28, 2011 at 10:38 pm

    @DM: Designated brokers in Canada are usually broker/dealers associated with the banks. In the US they include Goldman Sachs, Morgan Stanley, etc.

    In theory, I believe that large institutional investors such as pension funds can create and redeem PNUs (or creation units) directly with the ETF provider, but my understanding is that this does not usually happen.

  3. BC_Doc December 29, 2011 at 1:26 am

    @CCP: thanks for the informative article. Useful information to have as Vanguard rolls out its new ETFs. This information would make me less leery about purchasing a thinly traded ETF.

    Question for you: do you know how the bid-ask spreads are controlled? A large bid-ask spread will obviously make an ETF less popular since they adversely impact the transaction cost. How are the ETF providers keeping the spreads manageable on some of the thinly traded ETFs?

  4. Canadian Couch Potato December 29, 2011 at 9:55 am

    @BC_Doc: This is a good question. I’m going to look into the nuts and bolts further and report back in a future post.

  5. Arthur December 29, 2011 at 5:19 pm

    Thanks for diving deeper into ETF mechanics. Similar to what BC_Doc is asking, I’d like to know if DBs can do this arbitrage easily, do they have standing bid-ask orders a penny above and below the NAV? How fast is the tracking for ETFs, especially small-cap/low-volume ones?

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  7. Mark January 1, 2012 at 5:29 pm

    Like others, I’d love to know more about the buy/spread sells one sees on the lesser traded ETFs. For example, not unusual to see a consistent bid to buy 10,000 @ $9.50 with a simultaneous sell 10,00 $9.55 on a hypothetical ETF. Later in the day, that might have changed to buy 10,000 @9.54 Sell 10,000 @ 9.59 as the overall market has gone up by around half a percent (for example). After a 3% drop in markets overnight, the ETF opens at buy 10,000 @9.27 Sell 10,000 @9.32. etc etc etc. i.e. always equal buys of 10,000 from a market maker and always with the same or similar spread between bid and ask. As someone who wants to buy or sell this ETF, what would be the appropriate strategy for placing an order?

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  10. Dan Hallett January 11, 2012 at 5:11 pm

    I don’t think I’ve seen it linked up above but the video linked below is the only promotional twitter post I’ve clicked on in the three years I’ve been using the site. The video, by iShares, does a great job I think of explaining creation and redemption.

  11. Canadian Couch Potato January 11, 2012 at 7:57 pm

    @Dan H: I showed this to my wife to teach her about ETFs, but her response was, “How come you don’t buy me flowers?”

  12. Dan Hallett January 12, 2012 at 8:23 am

    Good one – and thanks for the heads up!

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