The best time to visit Liverpool is late spring to early autumn (May to September), when temperatures are most comfortable, the waterfront terraces come alive, and the city's packed events calendar — including Mersey River Festival in June and Liverpool International Music Festival in August — is in full swing.
May and June offer long daylight hours (up to 17 hrs), mild temperatures (14–18 °C), and smaller crowds than the summer school-holiday peak in July and August. September is a sweet spot: quieter, often sunny, and with the new cultural season getting under way.
July and August are the warmest months (averaging 17–20 °C) and coincide with school holidays, so popular attractions can be busier and accommodation pricier — book well ahead.
October to April brings grey skies and cooler temperatures (4–12 °C) but also some compelling reasons to visit: Gothic season around Halloween, the stunning Magical Lantern-style Christmas markets in November–December, and Rock 'n' Roll half-marathon events. Because most of Liverpool's top attractions are indoors and free, the city is a perfectly valid winter-break destination.
Avoid the weekend of the Grand National at Aintree Racecourse (early April) unless you plan to attend — hotels sell out city-wide and prices spike sharply.