Employment Litigation · Primary-source case analysis

Gross: An ADEA Plaintiff Must Prove But-For Causation

By Aneeta Mishra and Timothy Chan

Published May 2, 2026

Gross v. FBL Financial Services distinguishes the ADEA's causation language from the mixed-motive framework Congress adopted for certain Title VII claims.

The employee alleged an age-driven reassignment

Jack Gross claimed that his responsibilities were transferred to a younger employee and that the restructuring amounted to unlawful age discrimination. A jury instruction allowed liability if age was a motivating factor unless the employer proved it would have acted the same way anyway.

The statutory phrase controlled

The Court focused on the ADEA's prohibition against an adverse action taken because of age. It read that language to require proof that age made the difference—meaning the challenged action would not have occurred but for the employee's age.

The burden of persuasion stays with the plaintiff

Unlike the amended Title VII provision addressing motivating factors, the ADEA did not contain comparable text shifting the persuasion burden to the employer. The plaintiff therefore retains the burden of proving but-for causation throughout the case.

The judgment was vacated

Because the jury instruction used the wrong causation and burden-shifting framework, the Court vacated the judgment and remanded. Gross did not eliminate the use of circumstantial evidence or the McDonnell Douglas method in appropriate ADEA cases.

Key takeaways

• Identify the statute governing each discrimination claim.
• Frame ADEA causation as a but-for inquiry.
• Use direct and circumstantial evidence to test the employer's explanation.
• Do not import Title VII's statutory mixed-motive rule into the ADEA.