Direct Answer
This page is Swoopr Investment's maintained source for the U.S. equity-market rules most often referenced in order-routing and fill-quality education. Regulation NMS Rule 605 governs execution-quality disclosure by market centers. Rule 606 governs order-routing disclosure by broker-dealers. Rule 611 requires trading centers to prevent trade-throughs of protected quotations, subject to exceptions; it does not guarantee that every order fills at the NBBO snapshot the customer saw. Rule 612 addresses minimum pricing increments. FINRA Rule 5310 imposes a separate best-execution duty on FINRA-member broker-dealers that applies throughout the order-handling process. Every Swoopr execution guide should cite this page for rule mechanics rather than maintaining its own slightly different legal summary.
Rule 605: Execution Quality Disclosure
| Rule identifier | Regulation NMS Rule 605 (17 CFR 242.605) |
|---|---|
| Official name | Disclosure of Order Execution Information |
| Regulator | SEC |
| Status | Current (amendments adopted 2024 expanded covered entities) |
| Effective date | Original: 2001. 2024 amendments: phased implementation |
| Last Swoopr review | September 7, 2026 |
What it requires
Rule 605 requires covered reporting entities to publish monthly execution-quality statistics for covered orders in NMS stocks. Statistics include effective spread (the actual cost of execution relative to the NBBO midpoint at the time of order receipt), price improvement rates, fill rates, and speed of execution, broken down by order type and size range.
What it does not require
Rule 605 does not require any specific level of execution quality. It is a transparency rule: it compels disclosure of what actually happened, not a performance floor. A market center that consistently posts poor effective spread figures is compliant with Rule 605 as long as its reports are accurate and timely.
Scope
Applies to covered reporting entities, including market centers that execute covered orders in NMS securities. The 2024 amendments to Rule 605 expanded the definition of covered reporting entities.
Common misunderstanding
Rule 605 statistics are aggregate monthly figures across all orders of a given type and size range. They describe the distribution of outcomes across many orders under varying conditions. They cannot predict with precision what will happen on any individual order, and they should not be read as a guaranteed price or fill time.
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Rule 606: Order Routing Disclosure
| Rule identifier | Regulation NMS Rule 606 (17 CFR 242.606) |
|---|---|
| Official name | Disclosure of Order Routing Information |
| Regulator | SEC |
| Status | Current (significant amendments effective 2020) |
| Effective date | Original: 2001. 2020 amendments substantially revised disclosures |
| Last Swoopr review | September 7, 2026 |
What it requires
Rule 606 requires broker-dealers to publish quarterly reports identifying the top venues that received their non-directed customer orders, broken down by order type (market, limit, other). Reports must disclose material relationships between the broker and each venue, including whether the broker receives payment for order flow from that venue.
What it does not require
Rule 606 is a routing-transparency rule, not a fill-quality guarantee. It identifies where orders went and whether financial relationships exist that might influence routing. It does not by itself establish whether routing was appropriate or whether fills were competitive. Evaluating routing quality requires pairing Rule 606 routing data with Rule 605 execution quality statistics for the venues named.
Scope
Applies to broker-dealers registered with the SEC. Non-directed orders are orders where the customer did not specify a particular venue; directed orders (where the customer specified routing) are reported differently under the rule.
Common misunderstanding
A Rule 606 report showing payment for order flow to a given venue does not by itself establish a best execution problem. PFOF is currently permitted in the U.S. provided the broker maintains appropriate supervisory systems to ensure the arrangement does not override its best execution obligations. The question the data supports is whether the broker's routing to PFOF venues produces competitive execution quality for customers.
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Rule 611: Order Protection (Trade-Through Rule)
| Rule identifier | Regulation NMS Rule 611 (17 CFR 242.611) |
|---|---|
| Official name | Order Protection Rule |
| Regulator | SEC |
| Status | Current |
| Effective date | 2007 |
| Last Swoopr review | September 7, 2026 |
What it requires
Rule 611 requires trading centers to maintain and enforce written policies and procedures reasonably designed to prevent trade-throughs of protected quotations in NMS stocks. A trade-through is an execution at a price that is inferior to a protected quotation displayed by another trading center at the time of the transaction.
What it does not require
Rule 611 does not require that every market order fill at the exact NBBO snapshot a customer saw at the moment they submitted the order. Markets move continuously, and the NBBO at the time an order reaches the trading center may differ from the NBBO at the time the customer entered the order. Rule 611 also does not guarantee price improvement; it sets a floor against trade-throughs, not a ceiling on what execution must look like above that floor.
Important exceptions
Rule 611 contains several statutory exceptions where a trade-through does not violate the rule even though it would otherwise be prohibited. These include the intermarket sweep order (ISO) exception, the flickering quotation exception, the benchmark trades exception, the stopped order exception, and others. Understanding which exception applies requires reviewing the specific transaction type and the policies of the trading center involved.
Scope
Applies to trading centers that execute transactions in NMS stocks. A protected quotation is a displayed, immediately accessible top-of-book quotation at a trading center that has registered as a national securities exchange or an ATS displaying quotations in an NMS stock. Not all quotations are protected quotations for purposes of Rule 611.
Common misunderstanding
Rule 611 is sometimes described as a rule requiring execution at the NBBO. It is not. It prohibits trade-throughs of protected quotations, subject to exceptions. The NBBO is the reference benchmark most commonly associated with the rule, but the rule's protections apply to protected quotations specifically, and several categories of transactions fall within the rule's exceptions and do not constitute prohibited trade-throughs even when they appear to execute away from the NBBO.
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Rule 612: Minimum Pricing Increments
| Rule identifier | Regulation NMS Rule 612 (17 CFR 242.612) |
|---|---|
| Official name | Minimum Pricing Increments |
| Regulator | SEC |
| Status | Current (tick-size reforms ongoing as of 2026; verify current status) |
| Effective date | 2007 (penny pricing for most NMS stocks) |
| Last Swoopr review | September 7, 2026 |
What it requires
Rule 612 restricts market participants from displaying, ranking, or accepting quotations in NMS securities priced in sub-penny increments for securities priced at or above $1.00. The rule was intended to rationalize quoting conventions and reduce certain gaming behaviors associated with sub-penny quoting.
What it does not prohibit
Rule 612 does not prohibit sub-penny price improvement on customer executions. SEC guidance confirms that market makers and internalizers may execute customer orders at sub-penny price improvements even though sub-penny quoting is restricted. Sub-penny improvement is therefore a permissible benefit a market maker may provide; it is not universally required on every execution.
Common misunderstanding
Because Rule 612 restricts sub-penny quoting, customers sometimes assume that any fill with sub-penny components is irregular. In fact, price improvement to the sub-penny level is explicitly recognized in SEC guidance as something market centers may provide. The restriction applies to the displayed quotation, not to the execution price.
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FINRA Rule 5310: Best Execution
| Rule identifier | FINRA Rule 5310 |
|---|---|
| Official name | Best Execution and Interpositioning |
| Regulator | FINRA |
| Status | Current |
| Effective date | Predecessor rules date to NASD; FINRA Rule 5310 effective 2012 |
| Last Swoopr review | September 7, 2026 |
What it requires
FINRA Rule 5310 requires FINRA-member broker-dealers to use reasonable diligence to ascertain the best market for a security and to buy or sell in such a market so that the resultant price to the customer is as favorable as possible under prevailing market conditions. The rule specifies several factors relevant to determining reasonable diligence: the character of the market for the security, the size and type of transaction, the number of markets checked, and accessibility of the quoted price. The broker must also conduct regular and rigorous review of execution quality.
What it does not guarantee
Rule 5310 is a process standard, not an outcome guarantee. A broker that follows a documented, defensible routing process that accounts for the rule's factors satisfies the obligation even if a hypothetically better price existed elsewhere at the same moment. Regulators evaluate best execution through patterns across many orders over time, not typically through isolated individual trades.
Scope
Applies to FINRA-member broker-dealers when handling customer orders. Best execution obligations may differ by asset class: Rule 5310 applies to equity securities. Options have their own framework; fixed income, forex, and crypto assets traded on unregulated platforms have weaker or different frameworks. Verify the applicable framework for each product type.
Relationship to Regulation NMS
FINRA Rule 5310 and Regulation NMS Rule 611 are independent obligations. Rule 611 targets trading centers and prohibits trade-throughs. Rule 5310 targets broker-dealers and requires them to seek favorable terms for customers. A broker-dealer can route an order to a trading center that executes it within Rule 611's requirements while still potentially falling short of the Rule 5310 best-execution standard. The two rules occupy different positions in the order-handling chain: one at the routing decision, one at the execution.
Common misunderstanding
Best execution is sometimes conflated with the NBBO or with Rule 611 compliance. Best execution under FINRA Rule 5310 is broader than quote protection: it requires evaluating price, speed, likelihood of execution, and the full cost of the transaction, and applying that evaluation across the available markets for the security at the time of the order. A fill at or inside the NBBO does not by itself establish that best execution was achieved; and a fill that is technically consistent with Rule 611 does not by itself prove that the broker met its Rule 5310 obligations.
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How These Rules Connect
These five rules occupy different positions in the order-handling chain. A retail equity order passes through all of them, but no single rule covers the entire journey.
Rule 606 operates at the broker-dealer level before the order is routed: it creates disclosure obligations about where orders habitually go and what financial relationships exist at those venues. Rule 5310 also operates at the broker-dealer level, imposing a duty of reasonable diligence throughout the routing decision and the ongoing supervisory review of routing quality.
Rule 611 operates at the trading center level, once the order arrives. It constrains where the trading center can execute the order in relation to protected quotations displayed by other trading centers. Its exceptions define the categories of orders or circumstances where a transaction that might otherwise look like a trade-through is permissible.
Rule 612 governs the pricing granularity of quotations at the trading center level, affecting the minimum increment at which a market center can display a quote, while leaving room for sub-penny execution to benefit customers.
Rule 605 governs what the trading center reports about the results of all these decisions in aggregate, providing the data that makes the others checkable over time.
A customer evaluating execution quality uses these rules in reverse order: Rule 605 data shows what happened; Rule 606 data explains where orders went; Rules 611 and 612 explain the structural constraints on what the trading center could do; and Rule 5310 provides the framework for asking whether the broker's overall process was appropriate.
Frequently asked questions
What is the difference between Rule 611 and FINRA Rule 5310?
Rule 611 (the Order Protection Rule) is a Regulation NMS rule that applies to trading centers. It requires trading centers to maintain policies and procedures reasonably designed to prevent trade-throughs of protected quotations, subject to the rule's exceptions. FINRA Rule 5310 (Best Execution) applies to broker-dealers that are FINRA members. It requires those firms to use reasonable diligence to ascertain the best market and seek the most favorable terms reasonably available for their customers' orders. Rule 611 governs where orders go at the trading center level; Rule 5310 governs the duty a broker-dealer owes its customer in routing and handling that order. They operate independently, and compliance with one does not guarantee compliance with the other.
Does Rule 611 guarantee that every order fills at the NBBO?
No. Rule 611 requires trading centers to prevent trade-throughs of protected quotations, but a trade-through is a specific concept: executing a trade at a price inferior to a protected quotation displayed by another trading center. The NBBO a retail customer sees at the moment they submit an order is not a price-guarantee. Market orders may fill at prices that differ from the NBBO snapshot the customer saw because markets move continuously, quotes update between the time an order is submitted and the time it reaches the trading center, and the exceptions in Rule 611 (including the intermarket sweep order exception) allow certain executions that might otherwise appear to be trade-throughs.
What does Rule 605 actually measure?
Rule 605 requires covered reporting entities (market centers) to publish monthly statistics on execution quality for covered orders in NMS securities. The statistics include effective spread, price improvement rates, fill rates, and speed of execution. These are aggregate statistics over a reporting period for a category of orders, not a record of any individual fill. A retail customer can use Rule 605 data to compare execution quality across market centers where their broker might route orders, but the data reflects averages across many orders under varying conditions, so it is a directional signal rather than a precise prediction for any single trade.
What does Rule 606 tell a customer about their broker?
Rule 606 requires broker-dealers to publish quarterly reports disclosing the top venues that received their non-directed customer orders, separated by order type, and the material relationships between the broker and those venues, including whether the broker receives payment for order flow from each venue. This tells a customer where their orders tend to go and whether the broker has financial relationships with those venues that might affect routing decisions. It does not tell the customer whether their individual fills were good or bad; that comparison requires pairing the Rule 606 venue list with the venue's Rule 605 execution quality statistics.
What does Rule 612 say about sub-penny price improvement?
Rule 612 addresses minimum pricing increments, restricting certain sub-penny orders and quotations. However, SEC guidance clarifies that market makers and internalizers may provide sub-penny price improvement on customer orders in securities priced at or above $1.00 even though quoting in sub-penny increments is restricted. Sub-penny price improvement is therefore permitted as a benefit to the customer in certain contexts, but it is not universally required. Whether a given broker-dealer provides it depends on their routing relationships and the policies of the market centers they use.
Are dark pools and ATSs covered by Rule 611?
The relationship between off-exchange venues and Rule 611 is more nuanced than a simple exemption. Trading centers that operate as ATSs or internalizers must still maintain policies and procedures reasonably designed to prevent trade-throughs of protected quotations from other trading centers when they execute orders. However, the specific way Rule 611 applies to different trading center types depends on the venue's registration, the order type, and applicable exceptions. Off-exchange venues that execute retail orders are also subject to the best execution duty under FINRA Rule 5310, which requires them to seek the most favorable terms available under prevailing market conditions.
References
Regulatory source date: This page was reviewed against SEC and FINRA source material current as of September 7, 2026. Market-structure rules and reporting requirements can change. For compliance or legal interpretation, verify the current rule text and regulatory guidance directly with the SEC, FINRA, the relevant exchange, and qualified counsel.
- SEC: Frequently Asked Questions about Rule 605 of Regulation NMS
- SEC Release 34-51808: Regulation NMS Final Rule
- SEC Division of Market Regulation: Regulation NMS Rules 610 and 611 FAQ
- SEC Division of Market Regulation: Sub-Penny Rule (Rule 612) FAQ
- SEC: 2018 Rule 606 Amendments (Disclosure of Order Handling Information)
- FINRA Rule 5310: Best Execution and Interpositioning
- FINRA Regulatory Notice 15-46: Best Execution
Related guides
- Best Execution: What Brokers Owe Customers: the broker-level duty under FINRA Rule 5310 explained in detail
- NBBO and the Order Protection Rule Explained: how the NBBO benchmark relates to Rule 611 and to retail fill prices
- How Stock Order Routing Works: the mechanics of smart order routing and venue selection
- Execution Quality Comparator: use Rule 605 data to compare execution quality across venues
- Market Structure & Trade Execution: the full execution education hub
Educational disclaimer
For education only; not personalized investment, legal, or compliance advice. Trading can result in substantial losses. Broker-dealer rules, regulatory requirements, and SEC and FINRA rulemaking are subject to change. Verify current requirements with FINRA, the SEC, your broker, or a qualified professional before acting on this information.