Cost to borrow (CTB) is the annualized rate a broker charges to lend out SCAL shares for short selling. It varies throughout the trading day based on supply and demand.

Borrow fees rise when fewer shares are available to lend and fall when supply grows. Low-float, high-interest names often show sharp intraday fee spikes.

finshort polls IBKR throughout each trading session. Borrow fees and shortable share counts are refreshed every few minutes during market hours.