Here's what you need to know about using Costco to book your next vacation

Did you know that in addition to being able to shop in bulk for peanut butter and toilet paper, your Costco membership also grants you access to a travel agency?

It's true. Costco has an extensive travel program for its members, focusing heavily on packaged hotels, cruises and rental cars. And before you say that those types of vacations are not for you, consider that they can offer a really good value.

"It's a big world out there, and if travelers can't find the time to plan their perfect trip, packaged tours or vacations are a great way to ensure you hit all the highlights," Alex Howard, lead editor of Lonely Planet's homepage and interests, tells CNBC Make It.

In fact, if you're on a budget, Costco offers a rotating selection of "$499 and under" deals, where you can get an entire vacation for under $500 per person. Right now, Costco is offering a four-night cruise to the western Caribbean aboard the Norwegian Pearl in an ocean-view stateroom for $449 per person.

But before you hit the "book now" button, here are eight things you need to know about planning your next trip through Costco Travel.

You can browse Costco's travel deals, but to book one though the website or call center, you'll need to provide your Costco membership number. A basic membership to the wholesale club will set you back about $60 a year, according to the retailer's site.

If you plan to shop and travel with Costco frequently, then you may want to consider an executive membership, which is $120 a year. Executive members get 2% cash back on all Costco travel purchases. That's a benefit worth up to $1,000 a year.

Executive members also get access to exclusive travel deals and perks. For example, if you were to book a nine-night Moselle and Rhine river cruise that starts at $3,999 per person, executive members get a $50 per person shipboard credit.

For budget-conscious travelers, vacation packages are usually a "very good deal," Pauline Frommer, of travel-guide company Frommer's, tells CNBC Make It. When Frommer's was recently researching Cancun, Mexico and the Mayan Riviera, the team found people were saving, on average, 30-40% by booking a package for that destination.

Packages work best if you're travelling to a resorts, theme park destinations or a tourist-friendly capital city that has a huge number of hotels, Frommer says. But if you're going somewhere like Cleveland, you probably won't save as much with a package because there's less competition between the local hotels.

When it comes to getting the best rates on vacation packages, size matters, Frommer says. "Discounts are based on the clout of the middleman," she says. Negotiating rates usually comes down to how many rooms or airline seats or cabins the travel operator can guarantee it will move if it gets a good discount.

So in this regard, Costco may be at a disadvantage, since the wholesale club may not have the scale of companies like Expedia. "I have not seen any evidence that the packages are better at Costco," Frommer says.

Costco only works with a select number of airlines, cruise lines, hotel chains and rental car companies. So if you're looking to rent a car with Hertz, for example, you may be out of luck. Or if you want to book an airline with a low-cost carrier like Norwegian Air Shuttle, you'll need to do that separately.

If you collect loyalty points for airlines and hotels, you may not get to collect them when you book through Costco Travel. Costco's site notes that you can enter loyalty numbers only for Avis, Budget and Enterprise.

The most valuable part of Costco's packaged vacation deals may be the extra freebies that it throws in, Frommer says.

These perks can include free breakfasts, activities and resort or shipboard credits. An extra like "kids eat free" could be worth several hundred dollars for a family, depending on the duration of the trip and the destination, Frommer says.

For car rentals, Costco really shines. The wholesale club offers one free additional driver at U.S. locations of Alamo, Avis, Budget and Enterprise for any car rental booked through Costco. Plus, if you make your reservation through the Low Price Finder, you can cancel without any penalty fee.

It's more difficult to score a budget-friendly vacation at theme parks these days. "The problem is Disney, and to a lesser extent Universal, have made it harder and harder to catch a break," Frommer says.

Frommer recommends that if you're booking a packaged vacation to a theme park, read the itinerary very closely. You may be signing up for a trip that includes admission to the theme park every day you're in Orlando, even on your first day when your flight doesn't land until 4 p.m.

"You really have to look very carefully at what you want to see and do, so you make sure you're not paying for things you're not using," she says. And if you want to visit both Disney and Universal in Orlando, it may be more cost-effective to book things separately, since the majority of vacation packages do not include admission to both parks.

You should shop around to guarantee that you're getting the best price. Frommer recommends checking flight costs for your travel dates and destination on Momondo and Skyscanner, which Frommer's found typically offer the best prices. For hotels, she recommends checking out prices on Booking.com. For cruises, usually CruiseCompete is the biggest online travel agent in the game.

If the Costco package comes in below the total cost of booking all the trip components separately — or fairly even, but provides extra amenities — then you can feel good about reserving it.

Costco's vacation deals change frequently, so if you don't see any that tempt you, you can customize your own package or check back for other offers. Chris Hendrix, who oversees the buying division at Costco Travel, told CountryLiving.com that the booking "sweet spot" for these trips is usually three to six months ahead of time.

There's weekly rotating deals that include vacation packages, shipboard credit offers on cruises and prepaid gratuity events. This week, members can save on trips to destinations such as Puerto Vallarta, Antigua and Tahiti.

Don't miss: 5 things you need to know about booking a budget airline ticket, according to experts

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