The amount of money owed by a spread better when holding open positions and they are in a negative position. This is the money you have on deposit with the spread betting company which you are not currently using (sometimes referred to as free equity). More information about Initial and Variation Margins is given here. If a position has moved unfavourably since it was opened, a deposit further to that paid as the initial margin may be required in order to keep the position open (known as a ‘margin call’). Variation margin is also known as ‘maintenance margin’.