Costco can be a great place to find good deals on the foods you eat every day. But there are a few areas where your local grocery store or a big box store like Walmart and Target can offer better value for your money.
That's especially true when it comes to size. Because Costco generally sells products in bulk, to get the most out of your purchase, you need to make sure you can consume the larger quantities of a product before it goes bad. For ordinary families or individuals, that can be a high bar to clear.
That's primarily why Charlene Haugsven, founder of MyFrugalAdventures.com, tells CNBC Make It, "Just because Costco has it doesn't mean it's a bargain."
Here are the eight types of groceries she and other experts suggest that the average shopper should think twice before buying in bulk at Costco:
If you compare these items, especially the Kirkland brand, to similar products you'd find at the grocery store simply on price, Costco usually wins. However, the reason grocery experts put these items in the "don't buy" category comes down to the size.
The containers or packages are simply too big to end up being a good value for the average person.
Sure, some folks with big families, an extra freezer or lots of pantry space may think these are a good deal. In many cases, though, you'll end up throwing a good portion of the food away or struggle to find room for it in your home.
"A normal family is just never going to get through the quantity you have to purchase," Haugsven says. That's especially true on items like soy sauce, spice mixes and produce. If you live by yourself, springing for Costco's 1-pound container of fresh spinach, for example, may not make sense, though it is a steal at $4.99. That's because, even if it's stored properly, fresh spinach will usually only last 5 to 7 days in the refrigerator, according to shelf-life guide site StillTasty.com.
Large quantities can also be unwieldy to store. Though grocery stores usually sell flour in 5-pound sacks, Costco sells it in 25-pound packages, and it can be difficult to find space for all of that. "I would never want to store 25 pounds of flour. That's a whole year's worth of flour in advance," Haugsven says.
For other items, such as cereal, milk and eggs, you can find normal quantities of these items at similar prices at your local grocery or big box store during a sale. For example, Haugsven reports she buys the typical dozen eggs at Walmart for 32 cents an egg. Her local Costco sells eggs for 31 cents each, but you have to buy them in quantities of two dozen at a time.
Cereal, especially the name brand variety, is also often a good buy at your local grocery store, big box store and even at the drugstore. "Your grocery store is going to have big sales around cereal. One week it's going to be General Mills, another week it will be Kellogg," Joanie Demer, co-founder of The Krazy Coupon Lady, tells CNBC Make It.
If you're willing to shop around those sales, you're going to pay less.
Overall, "I think everyone is getting super competitive with Costco and I don't think, in order to save money on your groceries, you necessarily have to shop there," Haugsven says.
To get into the store for occasional trips, you can use a hack like bringing a gift card — but to make a habit of shopping at Costco, you usually need to purchase a membership, a basic version of which costs $60 a year.
Over 94 million members pay to access the chain's best products. And there's no denying that membership grants you access to some great deals. Costco typically doesn't mark up products more than 14 percent, whereas grocery stores mark up more in the range of 25 percent, Demer says.
Still, Demer says, it pays to diversify a bit and have a routine that includes multiple stores. "If you shop at Costco, you need a second place to shop," she says. "Otherwise, I'm willing to bet you're buying enough things that aren't good deals that you're kind of wasting the savings you're acquiring."
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