Margin interest is accrued daily and charged once a month. Annual margin interest varies based on your outstanding margin balance. Your daily margin interest is the effective margin annual interest / 360 * your overnight margin balance. If you do not hold any margin balance overnight, then there will not be any margin interest generated. 

Please visit: https://www.tradeup.com/pricing/commissions-us to view the most updated effective annual margin interest with TradeUP Securities.