How is seniority determined in the workplace?

What all seniority calculations have in common is that they measure, in some fashion, an employee's longevity with a company. Collective bargaining agreements usually calculate seniority by total length of service, sometimes with consideration for length of service within a particular craft or department.

What does the law say about seniority?

The employee is entitled to the seniority and seniority-based rights and benefits that he or she had on the date the uniformed service began, plus any seniority and seniority-based rights and benefits that the employee would have attained if he or she had remained continuously employed.