Sub-Penny Rule (SEC Rule 612)
The Formal Definition
A US SEC regulatory mandate under Regulation NMS prohibiting public lit exchanges from displaying or accepting orders priced in increments smaller than $0.01 for stocks trading above $1.00.
Lit Exchange Minimum Tick = $0.01 | Off-Exchange Internalizer Trading = Sub-Penny Allowed (e.g., $0.0001)
Cole Barrett's Reality Check
The Unvarnished Bottom Line"Rule 612 is the structural loophole that built high-frequency internalizers. Lit exchanges like the NYSE are legally barred from quoting stocks in fractions of a cent; they must move in whole pennies. Wholesalers operating off-exchange are exempt, stepping in front of lit quotes by $0.0001 to capture retail flow."
Interactive Simulator: Test the Math
Real-World Example: Scenario Breakdown
Examining the real numbers for: 1,000 shares of a $50 stock (Lit Exchange Spread: $50.00 Bid / $50.01 Ask)
| Execution Metric | Resting Lit Exchange Limit Order | Off-Exchange Wholesaler Execution |
|---|---|---|
| Fee / Rate | $1.00 fee | $0.00 'free' |
| Spread / Buffer | Legally restricted to whole penny ticks ($50.00) | Wholesaler quotes off-exchange sub-penny fill: $50.0001 |
| Execution / Status | Waits on public exchange book | Stepped in front of lit queue by 1/100th of a cent |
| Total Cost / Result | Bound by statutory tick size rules | Internalized order flow ahead of public lit markets |
How Brokers Weaponize This Term
Market-making wholesalers use sub-penny pricing flexibility to step ahead of resting public exchange orders by tiny fractions of a cent, capturing retail orders while bypassing public queue priority.
Broker Evaluation Matrix
Cole Approves
Interactive Brokers: Routes directly to public exchange order books, utilizing midpoint orders to compete with off-exchange pricing.
Read Audit →Cole Flags / Avoids
PFOF Zero-Commission Apps: Routes flow to wholesalers that exploit sub-penny rules to internalize retail volume.
View Trap Details →Frequently Asked Questions
Why was the sub-penny rule introduced?
To prevent high-frequency traders from stepping in front of customer limit orders by tiny fractions of a cent ($0.0001) without offering meaningful price improvement.
Does the sub-penny rule apply to penny stocks?
No. Securities priced below $1.00 per share are legally permitted to trade in sub-penny increments down to $0.0001 on public exchanges.