When to come — and when to absolutely avoid
By season
Quietest: November to February (excluding Christmas–New Year and the Three Kings' weekend in early January). Madrid winters are mild and the museum becomes a refuge from the chill outside.
Busiest: April–June and September–October are the peak tourist seasons. August is paradoxically quieter than expected because Madrileños leave the city — but it's also extremely hot and many shops nearby close.
By day of the week
Tuesday and Wednesday mornings are calmest. Mondays are surprisingly busy because some other museums are closed. Saturdays and Sundays are packed all day.
By time of day
The first slot at 10:00 is the quietest hour of the day — often you can stand alone in front of Las Meninas. The next sweet spot is 16:00–18:00, when morning tour groups have left and free-admission queues haven't started yet. Avoid the 11:00–13:30 peak when most groups arrive, and the free-admission windows (18:00–20:00 weekdays, 17:00–19:00 weekends) unless you specifically want them.