Orders & order types

An order is your instruction to open or close positions. This page covers the order types, how each one fills, and the rules specific to SPX options.

Anatomy of an order

Every order has:

• A type — market, limit, or stop.
• One or more legs, each naming an instrument, a quantity, and an action.
• A price effect — whether the net order is a debit (cash out, you're net buying) or a credit (cash in, you're net selling). Limit and stop orders also carry a price.

Leg actions

Action	Effect	Cash
Buy to open	Opens a long position	Debit
Sell to open	Opens a short position	Credit
Buy to close	Closes an existing short	Debit
Sell to close	Closes an existing long	Credit

To close a position, submit the opposite actions to the ones that opened it.

Order types

Market

Fills immediately at the natural price — the ask when you're buying, the bid when you're selling. Market orders must be single-leg; a market order with more than one leg is rejected.

Limit

Sits pending until the fill price meets your condition:

• Credit (selling): fills when fill price ≥ your price.
• Debit (buying): fills when fill price ≤ your price.

The fill price is the mid-based execution price described in How fills are priced (not your limit). If the market already satisfies the condition when you place it, it fills right away at that execution price; otherwise it waits. Limit orders are the only type that may have more than one leg.

Stop

A single-leg pending order that triggers when the mid crosses your stop level, then fills at the execution price:

• Credit stop: triggers when mid ≥ trigger (enter on a rally).
• Debit stop: triggers when mid ≤ trigger (enter on a pullback).

A stop that would trigger the instant you place it is rejected — set the trigger on the correct side of the current mid. Stop orders, like market orders, must be single-leg.

Multi-leg

Spreads, iron condors, butterflies, and any other multi-leg structure are submitted as one limit order (only limit orders may be multi-leg). Each leg produces its own trade record, but the order is atomic — all legs fill together or none do, and the fill is priced on the combo's net price.

How fills are priced

The execution price comes from the bid/ask using CBOE-style tick rules (the tick sizes are in SPX option price ticks):

Order	Fill price
Market	The natural price — ask for a buy, bid for a sell
Limit (single)	The mid, unless the bid/ask is exactly one tick wide (then the natural price), or the spread is an odd number of ticks (then the mid rounded one tick toward the market maker — up for a debit, down for a credit)
Limit (multi-leg)	The net price of the combo under the same even/odd-tick rule
Stop (on trigger)	Same as a single-leg limit

Worked example (single leg, nickel tick): a $2.40 / $2.55 quote is 3 ticks wide, so the mid $2.475 rounds in the market maker's favor — a buy fills at $2.50, a sell at $2.45. A $2.40 / $2.60 quote is 4 ticks (even), so both sides fill at the mid $2.50.

Slippage

Slippage is a single per-account setting (in Settings → Simulator Costs) — a multiple of $0.05 from $0.00 to $1.00 that worsens your fill in the market maker's favor. New accounts start with $0.05 of slippage; you can change or clear it any time in Settings. It applies the same way across all three modes: backtests, live trading, and historical trading. There is no per-order slippage; the value configured on your account is resolved automatically when an order is placed.

It affects limit and stop orders only: the order fills once the mid has moved enough that the slippage-adjusted price reaches your limit, and the realized fill is the mid worsened by the slippage (a debit pays mid + slippage, a credit receives mid − slippage). It models real-world execution drag; market orders are unaffected (they already fill at the natural price).

Example: with $0.05 slippage configured, a buy limit at $2.50 will not fill while the mid is $2.50 (it would fill at $2.55). The mid has to drop to $2.45 so that $2.45 + $0.05 = $2.50 meets the limit — then the order fills at $2.50.

The order's stored execution price is the mid your order must reach to fill: your limit minus slippage for a debit, plus slippage for a credit.

SPX option price ticks

SPX option orders must be priced on the right increment:

Order shape	Tick
Single-leg, price < $3.00	$0.05
Single-leg, price ≥ $3.00	$0.10
Multi-leg (2+ legs)	$0.05 always

The tier is set by the price itself: $3.00 and above uses the dime tick, so $3.00 and $3.10 are valid single-leg prices but $3.05 is not. Limit and stop prices that don't land on the correct tick are rejected before anything else is checked. Slippage, when supplied, must be a multiple of $0.05.

The maximum-profit cap

A limit order's price can't exceed the structural maximum profit of its legs — for example a $5-wide vertical caps at $5.00, because no more than that can ever be captured. This check is skipped when the maximum profit is unbounded, such as a naked long call or a ratio backspread.

Previewing an order

Before committing, you can preview any order: the ticket (and the API's dry-run endpoint) runs every validation and returns the projected fill price, fees, and buying-power impact without placing anything. A successful preview is a strong signal the real order will go through.

Canceling

Pending orders can be canceled before they fill. In a historical simulation, canceling removes the order and its associated trades and recomputes your history. In live trading, you can also atomically cancel-and-replace a pending limit order's price in a single step.