Why Don’t We Trade in Round Lots (or at least round off the shares)?

Over the last two years, you may have noticed that some of your individual stock holdings have gone from neatly-rounded share amounts, to odd-numbered share amounts. Why did this happen?

First, a little history.

In the days before computers, market specialists traded shares on paper in a physical stock exchange (think Trading Places). In order to make the math easier, they traded in what are called “round lots” or shares in multiples of 100. If you wanted to trade an odd lot back then, you would incur an additional cost. Once computers took over the trading landscape, odd-lot trading was no longer difficult. It’s just as easy for a computer to match round lots as it is for them to match odd lots, so there’s no extra fee associated with trading an odd lot. In addition, the advent of algorithmic trading has contributed to the increase in odd-lot trading.

Since there is no longer any impediment to trading odd lots, this is how we’ve purchased shares of stocks and ETFs for our clients for many years. Up until a couple of years ago, however, we still rounded off the share amounts to the closest 5 or 10 shares, primarily because those of us who work with numbers tend to appreciate evenly-rounded shares, neatly made beds, and spice cabinets where all the labels are lined up (and in my house, parsley/sage/rosemary/thyme must always be arranged thusly).

Alas, two years ago, our hospital corners came untucked by none other than a software program called iRebal. A fantastic program in so many ways, one of its features is, that it likes to calculate trades in dollars. This makes a lot of sense for the type of rebalancing that we do, which is always dollar-based. With our previous software, Portfolio Managers took an extra step to manually round-off the stock shares to the closest 5 or 10 before sending the trades to the blotter to be executed. iRebal saves the rounding to the last minute, so that it happens AFTER the trades reach the blotter. Prior to execution, the trader refreshes the stock prices and the share amount is calculated at that time. In this way, we are protected from buying or selling too much based on stale pricing. In addition, we found that having the software round the shares to the nearest 1 (rather than 5) resulted in a more accurate portfolio rebalance. And yes, we did have a lengthy discussion about switching to a nearest-one rounding convention, but decided that 1) since odd-lot trading does not result in a price disadvantage, and 2) it helps us achieve our stated rebalancing goals on behalf of our clients, it’s worth wrinkling the sheets a little bit.

Sarah DerGarabedian, CFA
Director of Portfolio Management

Sarah DerGarabedian

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