How much share trading happens in the dark, and what is the EU volume cap?

It depends on what you count. On the widest yardstick, "off-exchange" trading, the answer is now about half: in January 2025, off-exchange trading volumes in US equity markets surpassed on-exchange volumes, and over the whole of 2025 off-exchange trading reached a record 50.61% of US share volume, according to the broker Rosenblatt Securities. Dark pools proper are a smaller slice of that: 17.74% in 2025, by the same count. The rest includes wholesalers handling retail orders, and other trades arranged away from the exchanges.

Different yardsticks give different answers, and that is the first thing to understand. One estimate, from Tabb Group, put dark pools at 32% of trades in 2012, up from 26% in 2008. Another said that in 2012, 40% of equity volume took place in dark pools and internalizers, firms that fill orders from their own books. And the term "off-exchange" is wider than "dark pool", because it also includes those internalizers.

There is a twist about size, too. Dark pools were invented for big blocks, yet when the regulator FINRA began releasing quarterly data on these venues in July 2015, trades averaged 187 shares, which suggests the pools were not mainly used for large institutional trades.

Europe chose to cap it. MiFID 2, in force from 3 January 2018, introduced double volume caps: dark trading in a stock under the rules' waivers was suspended once, over the previous twelve months, one venue's share passed 4% of all EU trading in that stock, or all venues together passed 8%. The first suspensions hit hundreds of stocks. From October 2025 the double cap was replaced by a single volume cap of 7%.