Midpoint Discretionary Order (MDO)
The Formal Definition
An advanced exchange limit order type that rests as a displayed quote at the National Best Bid or Offer (NBBO) but carries a discretionary, non-displayed instruction to automatically execute against incoming orders up to the midpoint of the NBBO if contra-side liquidity appears.
Execution Range: Displayed Limit Price ≤ Fill Price ≤ Discretionary Midpoint Cap [ (NBBO Bid + NBBO Ask) / 2 ]
Cole Barrett's Reality Check
The Unvarnished Bottom Line"A Midpoint Discretionary Order is the chameleon of order types. It displays a quote at the bid to establish queue priority, but tells the exchange secretly: 'If a seller arrives and wants to meet in the middle, I am willing to pay up to the midpoint to get filled right now.' It balances passive queue priority with aggressive execution flexibility."
Interactive Simulator: Test the Math
Real-World Example: Scenario Breakdown
Examining the real numbers for: An investor buying 2,000 shares of a stock with an NBBO quote of $50.00 Bid / $50.10 Ask
| Execution Metric | Midpoint Discretionary Order (MDO) User | Static Displayed Limit Order Submitter |
|---|---|---|
| Fee / Rate | $0.0035/share DMA rate | $0.0035/share rate |
| Spread / Buffer | Submitted an MDO: displayed a buy bid at $50.00 with discretion to execute up to the $50.05 midpoint | Submitted a rigid, standard displayed limit buy order at $50.00 with zero discretion |
| Execution / Status | An incoming seller submitted a midpoint order; the exchange matching engine matched them instantly at $50.05 | Incoming seller refused to hit the flat $50.00 bid; stock drifted higher to $50.80 without filling the order |
| Total Cost / Result | Captured midpoint price improvement while maintaining resting limit queue presence | Missed execution due to lack of midpoint discretion |
How Brokers Weaponize This Term
When trading stocks with wide bid-ask spreads (e.g., 5 to 10 cents wide), use Midpoint Discretionary Orders (MDO). Displaying a quote at the bid preserves maker rebate eligibility while discretionary midpoint execution prevents you from missing fast breakout moves.
Broker Evaluation Matrix
Cole Approves
Interactive Brokers: Provides complete native support for advanced exchange-native order types including Midpoint Discretionary Orders across NYSE and Nasdaq.
Read Audit →Cole Flags / Avoids
Basic Mobile Retail Apps: Omits advanced discretionary order types, forcing retail users into basic limit orders that frequently miss midpoint execution opportunities.
View Trap Details →Frequently Asked Questions
Does an MDO display its midpoint discretion to the market?
No. The discretion to trade up to the midpoint is completely non-displayed and invisible to other market participants until an execution occurs.
Do MDO orders receive maker rebates?
If the order executes at its displayed price, it qualifies for standard exchange maker rebates. If it executes at the midpoint using discretion, exchange rules typically classify it as taking liquidity, incurring standard taker fees.