A pay difference can be lawful when it is based on a factor the applicable equal-pay law permits and the employer can show that the factor actually explains the difference. Under the federal Equal Pay Act, the statutory defenses are a seniority system, merit system, system measuring quantity or quality of production, or another factor other than sex. State laws may be narrower. Massachusetts, for example, lists six permitted categories, while New York requires a qualifying bona fide factor to be job related and consistent with business necessity. A label such as experience, market or merit is not enough by itself; the employer should be able to show how the factor was measured and applied.
Jurisdiction: United States
The Federal Equal Pay Act Has Four Statutory Defenses
The federal Equal Pay Act permits a wage differential where it is made under a seniority system, a merit system, a system measuring earnings by quantity or quality of production, or a differential based on another factor other than sex. These are affirmative defenses. That means the employer must be able to establish the defense when the Equal Pay Act's substantially-equal-work comparison is otherwise satisfied. Employers should therefore preserve evidence showing that the stated system or factor existed and actually affected the pay decision rather than identifying a justification only after a claim arises.
State Laws Can Narrow What Counts as a Bona Fide Factor
State equal-pay statutes often place more specific limits on lawful explanations. New York permits differentials based on seniority, merit, production systems or a bona fide factor other than protected-class status, but the bona fide factor must be job related and consistent with business necessity. Massachusetts uses a closed list that includes seniority, merit, production or sales systems, geographic location, job-related education, training or experience, and necessary travel. Employers should therefore map permitted factors by jurisdiction instead of relying on the federal phrase factor other than sex as a universal rule.
Experience Is Stronger When It Is Relevant to the Job
Experience is frequently used to explain why one employee is paid more than another, but the quality of the explanation matters. A defensible approach identifies the type and amount of experience relevant to the role, shows how the experience affected the employee's placement within the range and applies the same logic to comparable employees. Simply stating that one person had more experience can be weak if the experience was unrelated to the job or if the employer did not use the same criterion elsewhere. State laws may expressly require education, training or experience to be reasonably related to the particular job.
Merit Should Be Based on a Real System Rather Than Pure Discretion
A merit system is easier to support when performance criteria, review cycles, ratings and compensation consequences are defined before the pay decision. If managers describe merit differently for each employee, the employer may struggle to show that the differential resulted from a genuine system. Documentation can include performance evaluations, calibrated ratings, promotion criteria and merit-increase guidelines. Employers should also test whether the system is applied consistently across protected groups, because a formally neutral process can still create risk if discretion is uneven or unsupported.
Location and Market Factors Need Careful Jurisdiction Review
Geographic pay differences can be legitimate in some jurisdictions, especially where the statute expressly recognizes location or where the factor is job related and permitted. Employers should document how geographic differentials are established, such as approved market zones, cost-of-labor data or location-based salary structures. A broad statement that market conditions justified higher pay may be less persuasive without contemporaneous data showing which market was used and how it affected the employee's compensation. Because state statutes differ, location and market explanations should be tested against the specific law governing the employees being compared.
A Factor Should Explain the Difference, Not Merely Correlate With It
A lawful factor is strongest when the employer can connect it directly to the amount or structure of the pay difference. For example, if a salary range gives a defined premium for a credential, shift, supervisory duty or location, the employer can show how that premium affected pay. If the employer identifies several possible reasons but cannot show which one actually drove the difference, the explanation is less clear. Some state statutes expressly require the permissible factor or factors to account for the entire differential. Pay equity reviews should therefore test causation rather than simply collecting plausible labels.
Document Legitimate Factors at the Time Pay Is Set
The most reliable evidence is created during the compensation decision. Offer approvals, range-placement notes, performance records, job descriptions, experience matrices, geographic differentials and exception approvals can show why a particular salary was selected. The documentation should be proportionate and consistent, not a narrative written only after a dispute arises. Compensation governance can require managers to select from approved factors and provide supporting evidence for exceptions. That makes later audits more efficient and reduces the risk that similar pay decisions are explained differently depending on who made them.
Frequently Asked Questions
What are the four defenses under the federal Equal Pay Act?
Seniority, merit, a system measuring quantity or quality of production, and another factor other than sex.
Can experience justify a pay difference?
Potentially, but the applicable state law may require the experience to be job related, and employers should document how it affected the pay decision.
Is market pay always a lawful explanation?
No universal rule applies. Whether market or location factors are permitted and sufficient depends on the governing statute and the evidence connecting the factor to the differential.
Related Guides
Official Sources
Requirements and practices differ by jurisdiction and organisation. Check current local law, official guidance and professional advice for a specific situation.