Business Rules
A business rule is a statement that defines or constrains some aspect of how a business operates, such as who may approve a refund, how a price is calculated or when an account is suspended. Business rules exist independently of any software, but products have to enforce them, so teams capture and manage them as part of the requirements.
How Business Rules Work
The BABOK Guide defines a business rule as a specific, practicable, testable directive that is under the control of the business and guides behavior, shapes judgments or informs decisions. The important point is the origin: a rule comes from the organization (a policy, a regulation, a contract or a pricing decision), not from the design of a screen or a database.
Rules are commonly split into two kinds:
- Definitional rules state what a term means or how a value is derived. Example: "A customer is active if they placed an order in the last 90 days."
- Behavioral rules state what people or systems must or must not do. Example: "Refunds over $500 require manager approval."
The Business Rules Manifesto, published by the Business Rules Group in 2003, sets out the principles most practitioners follow. Rules are first-class requirements in their own right. They should be written declaratively, in plain sentences the business can read. They are not process or procedure and should not be buried inside either, because one rule usually applies across many processes. A rule is also separate from how it is enforced.
In practice, one rule may be enforced by several functional requirements across screens, APIs and background jobs. Teams keep rules in a catalog with IDs and reference those IDs from requirements, tickets and tests.
Why Business Rules Matter
Rules change more often than the workflows around them. Pricing, eligibility and compliance limits shift with strategy and regulation. When a rule lives only inside code or is copied into several tickets, a policy change means searching the codebase, and different parts of the product end up enforcing different versions. Keeping rules explicit lets business stakeholders review them without reading code, and makes them testable: every threshold in a rule implies test cases, and the values at its limits become edge cases.
Explicit rules also matter when AI coding agents write the code. An agent that is not told the rule will still choose something plausible, such as a rounding method or a default discount, and that choice becomes policy by accident. For guidance on stating rules and constraints precisely, see how to write clear, testable technical requirements.
Business Rules Example
A subscription product has the rule: "A trial account without a payment method is locked 7 days after sign-up." That single rule drives several requirements: a countdown banner, an email on day 6, a lock screen and an API check that blocks paid features. If the trial later becomes 14 days, the team updates the rule once and uses requirements traceability to find every place it is enforced.
Business Rules vs. Functional Requirements
A business rule states policy: "Orders over $1,000 need credit approval." A functional requirement states what the system does to support it: "The system shall hold orders over $1,000 in Pending Approval status and notify the credit team." A useful test is that the rule would still exist if the business ran on paper.