One-way mode is a position setting that maintains one net position for a contract: long, short or flat. Opposite-side executions reduce the existing position instead of creating a separate long and short record for that contract.
An order can close and reverse
Suppose a trader holds a three-unit long and a five-unit sell order fills completely. In ordinary one-way netting, three units close the long and the remaining two open a short. This example assumes the order is permitted and has no restriction preventing new exposure.
Where supported, a reduce-only instruction limits an order to reducing or closing the existing position. Any excess is handled under the platform’s rejection, cancellation or quantity-adjustment rules rather than opening the reverse side.
One direction does not mean one risk
The mode can simplify position records and makes the current net quantity clear. It does not prevent exposure to other contracts, assets or correlated markets elsewhere in the account.
One-way mode also differs from isolated margin: netting controls the position record, while margin mode controls how collateral supports risk. Fees apply to executed trades according to the venue, including closes and reversals. Before changing mode, check the product’s support and whether open positions or pending orders prevent the switch.