What does Marked to Market mean?

Marked to Market is how a broker updates the value of your open positions each day. At 16:00 ET, the closing price is used to calculate unrealized profit or loss, which is then added to or subtracted from your equity. The same process applies if you open a position after 16:00 ET.

For example, if you bought a stock at USD50 and it closes at USD55, the Marked to Market (MtM) value is USD55 and you would see an unrealized gain of USD5 per share added to your equity. If it closed at USD45, the MtM value is USD45 and you would see an unrealized loss of USD5 per share deducted.