Since the completion of Brexit, UK passport holders are subject to the Schengen Area 90/180-day rule. This means you can stay in Spain (and any other countries in the Schengen Zone) for a maximum of 90 days within any 180-day period without a visa. This is a "rolling" window; to calculate your allowance, you look back 180 days from any given day of your stay to ensure you haven't exceeded the 90-day limit. This rule applies to all forms of short-term visits, including tourism, visiting family, or attending business meetings. It is important to note that your passport must be "valid for at least three months" after the day you plan to leave, and it must have been "issued within the last 10 years" on the day you enter. If you wish to stay longer than 90 days—for example, to live, work, or retire in Spain—you must apply for a formal national visa, such as a Digital Nomad Visa or a Non-Lucrative Visa, through the Spanish Consulate in the UK before you travel. Overstaying the 90-day limit can result in heavy fines, deportation, and a potential ban from entering the entire Schengen Area for several years.