In Las Vegas, hotel room rates seem to shift like rolling dice. Sometimes you win and get a $199 rate in March at the Bellagio resort, and sometimes —including over St. Patrick’s Day weekend (this year from March 15 to 17) — you’ll pay $429.

Traffic in Las Vegas spikes over holidays like Chinese New Year, and events like the N.C.A.A. March Madness basketball tournament (March 19 to April 8). Add in 22,000 annual meetings that may draw as many as 175,000 attendees to a town with 150,000 hotel rooms, and you have a case study in travel economics: With crowds come higher prices. Conversely, fewer people often means lower prices.

“If you’re flexible with your dates, you can get so much more bang for your buck,” said Yves Marceau, the vice president of product at G Adventures, a tour company where spring itineraries to Europe, for example, can save 20 percent or more over summer trips.

Rather than strictly traveling in the off-season, when savings can be greatest but weather is often at its worst, the trick is to find soft periods in times of stronger demand. Cheaper travel varies widely by destination, but there are a few general guidelines to follow while planning. In addition to checking convention traffic (Las Vegas lists its meetings at vegasmeansbusiness.com), look for holidays in a foreign destination and probe airline booking calendars for soft travel days. Search engines like Kayak indicate “good days to travel,” meaning bargain days, and the airfare prediction app Hopper shows a calendar color-coded to pricing.