Glossary
What is the spread?
In one sentence
The spread is the gap between the highest price buyers will pay and the lowest sellers will accept. It is a real cost, even on "zero fee" platforms.
At any moment there is a best bid and a best ask, and the difference between them is the spread. Buy at the ask and immediately sell at the bid, and you lose that difference — before any commission.
This matters because it is where “commission-free” platforms usually make their money. A service advertising no trading fee may quote a spread several percent wide, costing you considerably more than a platform charging a visible 0.1% commission on a tight spread.
To compare honestly: check the buy price and the sell price for the same asset at the same moment on each platform. The round-trip difference is your true cost, and it frequently bears no relation to the advertised fee.
For example
A platform showing "0% commission" alongside a 3% spread is more expensive than one charging 0.2% on a tight one.