May, July, August and October — the late-May half-term, the UK summer holiday, and Scarefest in late October.
Quietest months
April, June and September — term-time weekdays in April, June and September.
Local knowledge: The entire UK crowd calendar is school terms. A Tuesday in mid-June and a Tuesday in August are effectively different parks.
How this is worked out
Each day starts from how that weekday normally runs at Alton Towers, learned from our own recorded wait snapshots as they accumulate, and is raised for public holidays and school-holiday periods. It is a forecast of relative busyness, not a promise: a 3 means a day that usually runs quiet for this park, not a guarantee of short lines. The further out a date sits, the more it leans on the weekday pattern alone.
Want the live picture instead? Alton Towers wait times has today's queues, the hour-by-hour curve and what counts as a normal wait here. Planning a specific day? Open the planner and it will build a route around these crowd levels.