Yes, you can trade in the same day if you deposit via ACH before 4:00 pm on a trading day. You will get a provisional credit (up to $1000 depending on the incoming deposit) of buying power after your deposit. You can use this provisional buying power to trade. Note that if you do so, your cash balance might go negative because you are using credit rather than settled cash. The deposit won't be added to your cash balance until it settles after 5 business days. You can review the settlement date and other details in the prompt on top of the "Trade" screen or in the "Deposit" section.