Want to be part of the action-packed forex market? You must be aware of several concepts, including free margin in forex. It’s a margin that you have available to open new positions. This can’t be used for existing positions, though. You will likely have more free margin if your price speculation turns out to be correct on most occasions. In case the market goes against your speculation, the free margin can drop significantly. It is calculated by subtracting the used margin from the equity.