For a visit to Auschwitz-Birkenau in 2026, you should book your entry passes exactly 90 days in advance if you are visiting during the peak season (May to September). The museum has strictly capped daily visitor numbers to preserve the site and ensure a respectful atmosphere, and "guided tour" slots often sell out within hours of being released on the official website. If you are an individual traveler looking for the "Free of Charge" tour slots (which are usually early in the morning or late in the afternoon), these are even more competitive and should be booked the moment they become available at midnight CET. For those visiting in 2026 during the "off-season" (November to March), booking 2 to 3 weeks in advance is usually sufficient. It is highly recommended to avoid third-party resellers unless the official site is completely sold out, as those "organized" tours often charge three to four times the official price for the exact same museum-led experience.