What is reduce-only order?

An order flag that permits an order to shrink or close an existing position but never to open or enlarge one.

Without it, a stop or take-profit left on the book after a position closes can flip you into a fresh position in the opposite direction, which is a common and expensive accident on derivatives venues. Reduce-only orders that would increase exposure are rejected or trimmed automatically.

The flag matters because exit orders and entry orders look identical to a matching engine. A stop-loss sell under a long position is just a sell order. Once the long is gone, that sell order is an instruction to go short, and the engine has no way to know you did not mean it.

How it works

1. You hold a position and place an exit order: a stop order below a long, or a take profit order above it.
2. The position closes by some other route. Perhaps another exit filled first, perhaps you closed manually, perhaps it was liquidated.
3. Your original order is still resting on the book. Without the flag, when it triggers it opens a new position in the opposite direction, using margin you may not have intended to commit.
4. With reduce-only set, the venue checks the order against your current position at execution time. If there is nothing to reduce, the order is cancelled or rejected. If the order is larger than the remaining position, it is trimmed to fit.

Most derivatives interfaces present it as a checkbox on the order ticket. Behavior on partial fills and on cancellation differs by venue, so check the exchange's own order-type documentation rather than assuming.

Example

Illustrative sequence. You are long 10 contracts. You set a take-profit sell for 10 above the market and a stop sell for 10 below it, neither marked reduce-only.

Price rises and the take-profit fills. You are flat, and you stop watching. Price then falls back through your stop level. That sell order triggers with no position to close, so you are now short 10 contracts, in a falling market you were never trading, with margin committed and a liquidation price you never calculated.

With both orders marked reduce-only, the stop is cancelled when it finds nothing to reduce. Same two orders, same price path, no accidental position. The venue's own bracket or one-cancels-the-other order types solve the same problem differently, where offered.

Why it matters when you buy

If your buying is spot only, this flag never comes up, and that is one of the plainer reasons spot is simpler. It matters the moment you use a derivatives venue, because it is the difference between an exit plan and an accidental trade. Availability of these products varies by jurisdiction, which the jurisdiction pages track, and the exchange directory covers what each venue offers.

Related terms

perpetuals — where the flag matters most; stop order — the usual exit that misfires; take profit order — the other half of a bracket; liquidation — what an unintended position risks; isolated margin — limits the damage of one; time in force — how long orders survive.

Questions

Do I need this for spot trading?

No. Spot orders spend balances you hold and cannot open a short, so there is nothing to guard against. It is a derivatives control.

What happens if my position is smaller than the order?

The venue trims the order to the remaining position size rather than executing the excess. That is the behavior on most exchanges, though the details of partial fills vary, so confirm on the venue you use.

Is it the same as a bracket order?

No. A bracket links entry and exit orders together, often cancelling one when the other fills. Reduce-only is a per-order constraint that works whether or not the orders are linked, and using both is common.