Initial margin = (position's opening price* trade size)* initial percentage of margin. For starters, let's say that you buy 30 Facebook CFD stocks for $75 each (a ‘Buy' position), then the position value will be 30*75= $2250. If the original margin percentage was 20%, then the initial margin needed would be 20% * 2250 = $ 450. Maintenance Margin = (position's opening price* trading size)* proportion of maintenance margin. For instance, let's assume that you buy 30 Facebook CFD stocks for $75 each (a ‘Buy' position), then the position value would be 30*75= $2250. If the percentage of the maintenance margin was 10 percent, then the maintenance margin needed will be 10 percent * 2250 = $ 225.