Spread cost calculator
A venue advertising “zero commission” still charges you. The charge is the spread, and it is quoted nowhere on the trade ticket.
Why basis points
A spread in dollars means nothing without the price it sits on. Twenty cents on a $100 asset is 20 basis points; twenty cents on a $2 asset is 1,000. Basis points are how spreads are compared, and how a “free” venue is compared with one charging an explicit fee.
Break-even
Buying at the ask and selling at the bid means the price must rise by the full spread before you are level. The tool reports that as a percentage: it is the hurdle every trade starts behind, before any commission.
What this does not model
Slippage on orders larger than the quoted size at the top of the book, and spreads that widen sharply in volatile conditions — which is precisely when people trade. The figure here is the best case. See spread and slippage.
