A business day is a unit of time that includes the operational hours of banks, financial markets, and government agencies. It is typically defined as any day that banks, government offices, and most businesses are open and operational, which is generally Monday through Friday, excluding weekends and any public holidays. The exact definition of a business day may vary depending on the specific business and industry, and it depends on the local workweek which is dictated by local customs, religions, and business operations. For example, in the United States and much of the Western world, business days are typically Monday through Friday from 9 a.m. to 5 p.m. In Mexico, the standard workweek is Monday through Saturday.

Business days are important because they define when something will be available or must be delivered. For example, banking transactions, shipping, contracts, and stock trades often reference business days. When conducting international transactions, individuals and companies should be aware that business days may vary by country due to a difference in the public holidays observed.