Many people still struggle to find the answer to: 'When is the best time to book your holiday?' Picture: Vacation Lists.

When's the right time to book your next vacation? At the peak of travel-planning season, that's a common question. 

This is the time of year when everything from holiday trips to spring-break cruises are being pulled together. But the best answer - besides a noncommittal "it depends" - usually is "as soon as possible."

Both of those responses can be frustrating. You need to know if there's a best time to pull the trigger. As it turns out, there is, but it depends on what you're booking, where you're traveling and when you're planning to go.

"There is no magic answer," says Michael Sheridan, an assistant professor at Temple University's School of Sport, Tourism and Hospitality Management. "There are a number of factors that impact the fluctuation of rates."

Travelers who book at the right time - wisely - can save hundreds on a ticket or room, while people who push the button at the wrong time can see their rates double. Here are some factors that can increase your odds of landing in the former category.

Airfares can be volatile all year. Prices are typically at their lowest point between three and four months before a departure. 

They jump 14 days before departure and again 7 days before you leave as computerised pricing systems anticipate higher demand from business travelers, who have more money to spend. Sure, last-minute sales happen often, but they are almost impossible to predict.

Hotel rates: Typically, hotel prices fluctuate far less than airfares, rising predictably when demand increases, then falling during slack times such as early January.

A recent rate analysis by the fare analysis site Yapta.com revealed that for hotels booked in May, there is a significantly higher probability that a price drop will happen; if you've booked a stay in November, prices are at their most stable. In some markets, prices are wildly unpredictable. The three cities with the greatest price volatility are London, San Francisco and New York, according to the site.

As with airlines, booking a room a week or more in advance could result in a lower rate. 

Car rentals: Here, too, pricing is highly dynamic, meaning it is driven by supply and demand, "with extreme elasticity as a function of day, date and even time of booking," says car-rental consultant Neil Abrams.

Cruise tickets: Highest seasons are around July and right around Christmas and early January, according to analysis by Seahub, a cruise-booking website. "So book right after these periods," advises Makoto Rheault-Kihara, the site's marketing director. 

Ticket prices sink in March and August because of low demand. Most tickets are sold during the traditional "wave" season early in the year, when rates can be at their highest. During winter, people are thinking about cruising to a warm-weather destination. Cruise lines and their marketing machines are trying to capitalise on your cabin fever.

Vacation rentals: This is one of the great travel mysteries, as prices are often set by owners rather than computer algorithms. 

Of course, all of this assumes the inventory of tickets, rooms and cabins is unlimited. It's not. When supplies run out, the game ends. So, in the end, that advice about booking early still rings true. If you absolutely have to be somewhere, book as soon as possible.