Is the 13th-month salary legally required in Switzerland?
Not by federal law as a universal right. The Swiss Code of Obligations doesn't mandate it for every employer. It becomes a binding entitlement only where it's explicitly agreed, in your individual employment contract, a company policy, or a Gesamtarbeitsvertrag (GAV, a sector-wide collective bargaining agreement). In practice, though, it's extremely common in Zurich and across Switzerland, especially in white-collar roles, so most job offers do include it even without a legal mandate.