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High frequency trading
Ask almost anyone what share of US stock trading is done by high frequency firms and you'll get a number, usually somewhere around half. It gets repeated in articles, books, documentaries and forum arguments. What I wanted for this page was the source of that number.
There isn't one. No US regulator or exchange has published a high frequency share of volume since around 2016. The SEC's own 2020 report on algorithmic trading contains no such figure. A 2022 speech packed with market structure statistics contains none. A 2025 data release explicitly leaves participant type breakdowns out. The last official figure is from a 2010 concept release, and the widely quoted 55% comes from a 2016 congressional report with no attribution at all. The absence is the finding here, and it took targeted searching of every place such a figure would live to establish it.
So this page collects every traceable estimate with its vintage and its producer, shows what the two genuine measurements from exchange data actually found, walks through what the evidence says about whether high frequency trading helps or harms, and covers what's known about the economics of the firms doing it. The notes at the bottom are unusually long because several of the most repeated statistics in this field could not be sourced, and I'd rather name them than pass them on. Five sources, all linked, most of them free.
No US regulator or exchange has published a high frequency trading share of volume since around 2016. The SEC's 2020 algorithmic trading report contains none. A 2022 speech dense with market structure statistics contains none. A 2025 data release explicitly excludes participant type breakdowns. The last official figure is the SEC's own more than 50% from a 2010 concept release, and the widely quoted 55% comes from a 2016 congressional report with no attribution at all. The best actual measurement, from regulator grade exchange data covering 26 named firms, gave 42% of volume in large stocks and 18% in small stocks for 2008 to 2009. The absence is the story.
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Below this point there are 9 sections, 1 chart and 5 named sources, roughly 2500 words of it. Every figure carries the source it came from and the date the data is from.
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