trading schedule is daily without carrying over night. Within the year, some more capital is injected to the account for doing larger position. My question is if we calculate the daily return by the difference of account value, it would be mis leading because of the capital injection would it be practical to use the intraday margin requirement when calculating the daily return? Say, the PnL is 500, the intraday margin is 20000, so the return is 1/40. To sum up, just use the capital required for the position. i don't know whether i m correct or not but seems making sense. Also, what is the standard daily risk free rate assumption ?