$2,000 – In order to carry a margin debit balance or engage in short selling, you must have at least $2,000 of margin equity in the account. If you don’t have that much in your account, you really shouldn’t be messing around with margin to begin with.
$25,000 – If you’re classified as a pattern day trader, your account must maintain $25,000 in account equity to continue day trading in the account. Failure to do so will result in a 90-day cash restriction. To remove the day-trader classification, you must go 60 days without completing a day trade.