Commission

Commissions were once the obvious cost of investing: a flat charge, or a charge per share, applied to every purchase and every sale. Most large US brokers cut them to zero on US-listed stocks and ETFs around 2019, and the industry has largely stayed there since.

Zero commission is not the same as zero cost. The bid-ask spread is still paid on every trade, funds still charge an expense ratio, and brokers still earn revenue in other ways, including interest on uninvested cash and payments from the firms that execute customer orders. Those costs are real. They are simply not itemized on the confirmation the way a commission was.

Commissions have not vanished everywhere either. Options contracts, trades placed over the phone with a person, some foreign markets, and transfers of an account to another firm commonly still carry one. Each broker publishes its own schedule, so the answer is in that document rather than in a general rule.