Spring and fall are the answer
March through May and September through November are the objectively best months for southern Nevada. Vegas averages 75 to 88 degrees, hotel rates hold at $150 to $250 midweek, and pool season is either opening or closing (October pool days are underrated). April brings EDC (Electric Daisy Carnival) — plan around it unless you are attending, rates triple. October has Life is Beautiful in downtown Vegas and perfect Red Rock hiking weather. Northern Nevada shoulders differently: May and September at Tahoe hit 70s during the day, empty trails, half the summer prices.
Summer, winter and the edge months
June through August: 105 to 115 degrees in Vegas, pool season peak, hotel rates paradoxically low midweek because leisure travelers avoid the heat. Tahoe hits its summer peak — book six months out. December through February in Vegas: 55 to 65 degrees, cheapest rates of the year (outside NYE and CES), no pool. Tahoe ski season November to April with best snow February to March. New Year's Eve on the Strip is legendary and awful in equal measure — 400,000 people, rooms from $600, closed roads. Book it if it is on the list, then never repeat.
Good to know
When is Vegas cheapest?+
First two weeks of December (post-Thanksgiving, pre-holidays) and last two weeks of January (post-CES). Rooms drop 40 to 60 percent.
Can you swim in Vegas in winter?+
Yes at heated pools — Waldorf Astoria, Aria and Resorts World keep at least one pool open year-round.