What is an algorithm in your definition?<p>If it includes where and how to place the trades (a smart order router) I would say 99% of trades are managed by an Algo. Also there are the &quot;dumb&quot; VWAP, POV, TWAP algos which represent the bulk of &quot;smart&quot; buyside money as internally most firms use vwap as benchmark.<p>The bulk of retail orders in the US are on the other side of an algo from citadel, knight or citi. And often buying 100 shares of MSFT at market only really needs a decent SOR to provide BestEx.<p>Block trading still often gets fed to VWAP algos unless the stock is illiquid.<p>Finally the most interesting execution algos (implementation shortfall algos) are hard to explain and only statistically outperform.<p>If you are talking about actual investing - the first question is which asset class in which to park your money. If you can get an algo to do that (like Renaissance) you will be rich.