Ever stop to figure out how much you spend on pet food each year? Any pet parent knows that kibble and chow can really add up. According to petfinder.com, the annual cost of feeding a dog or a cat ranges from about $120 to $500.

If you want to save money on pet food, it pays to shop around. A recent survey by Checkbook.org — published by the Center for the Study of Services, an independent, nonprofit consumer organization — found quite a price spread.

Checkbook shoppers compared prices for 11 popular dog and cat foods at a sample of pet stores, big-box discounters, grocery stores and warehouse clubs in seven metro areas: Boston, Chicago, Minneapolis-St. Paul, Philadelphia, San Francisco, Seattle and Washington, D.C. They also visited several national online retailers. Because stores often carry different-size packages, Checkbook shopped for the lowest prices on a per-pound or per-ounce basis for each product.

“The stores we shopped that offered the best prices charged about 40 percent less than the most expensive places,” said Kevin Brasler, Checkbook’s executive editor.

A table in the Checkbook report shows the prices found, along with their price comparison scores — how that retailer’s prices compared to the average prices for all companies surveyed.

"Among stores with local outlets, the lowest prices were consistently offered by the places that you'd expect: Walmart and membership warehouse clubs, Sam’s Club and BJ’s,” Brasler told NBC News BETTER. “We also found that Costco offers really low prices for pet food. Because it, for the most part, carries only its own Kirkland brand, we could not compare its prices to the others.”

So who has the lowest prices?

Sam’s Club’s prices were 22 percent lower than the all-store average.

BJ’s Wholesale Club was 18 percent lower.

Walmart was 12 percent lower.

PetSmart was about 2 percent lower.

Prices at Petco, Checkbook found, were about the same as the average.

ONLINE ISN’T ALWAYS THE CHEAPEST

Checkbook found that shopping online doesn’t always result in the lowest prices. All the websites in the report were more expensive than the price leaders: Sam’s Club, BJ’s and Walmart. But having that 50-pound bag of dog food delivered to your door is mighty convenient.

Checkbook found that:

Chewy.com was the least expensive online option, with prices about 11 percent lower than the all-store average.

Amazon’s prices for the products surveyed were 5 percent higher than average; more expensive than several other online retailers’ prices and about 18 percent higher than Chewy’s.

If you shop online, make sure you buy enough to get free shipping. Or order online and pick up at the store. With Petco, the discount for in-store pick-up is 10 percent; PetSmart is 5 percent.

Another money-saving option: Some online stores give a discount, typically 5 percent, if you sign up for their auto-ship program. Don’t worry, it’s easy to cancel, modify or suspend auto-ship orders.

Checkbook found that Chewy’s 5 percent auto-ship discount makes its prices competitive with the lowest-cost local outlets. Unfortunately, online retailers often exclude many products from their auto-ship discounts, Checkbook noted.

WHAT I FOUND WHEN I WENT PRICE-SHOPPING

I wanted to see first-hand, just how much prices varied from store to store where I live. I visited Costco, Fred Meyer (a Kroeger-owned store in Seattle), Petco, Safeway, Target and Walmart. I also went shopping for those same items online at Amazon, Chewy, Costco, Sam’s Club, Target and Walmart.

I found a few products that all the stores sold and a few that most sold. Whenever I had a choice, I selected the largest size. Then, I calculated the unit price, similar to what Checkbook did.

Here’s what I learned:

Prices are all over the place. For example, the price for Pedigree Complete adult dog food varied from 52 cents to $1.40 a pound.

In most cases, buying the bigger size will save money. If you’re in a store that only has small sizes, you may need to buy that item to tide you over for a few days, but for the long-term, this is not the way to go.

Don’t assume online prices are always lower than physical stores. They were for most items, but not all. And in doing my analysis, I assumed that I bought enough to get free shipping. If you’re paying for shipping, you may lose that price advantage.

Most retailers charged the same price for the same product both in-store and online, but not always. Also, in some cases, the sizes available online were different from what was available at the store.

The key takeaway I learned from this experience: Comparison shopping isn’t easy because the sizes available often vary from store to store.

When looking for the variety pack of Fancy Feast cat food, I found packages of 24, 30 and 60 cans. Most of the variety packs had 3-ounce cans, but one store had 5.5-ounce cans. The packages of Greenies (largest available at that store) were in 6, 8, 12, 27 and 36-ounce sizes.

The only way to know which store is selling the specific product you want for the lowest price is to use a unit price calculator. Just put in the price, the number of items and the weight, and you’ll get the per-ounce or per-pound price.

A FEW MORE MONEY-SAVING TIPS

There aren’t a lot of coupons for pet food, but it doesn’t take long to check the manufacturer’s or retailer’s websites, or visit a coupon website, such as RetailMeNot.

While pet food is something you need to buy year-round, be prepared to stock-up when you see coupons or spot a sale. The deepest discounts on dog and cat food are found around Memorial Day, at 19 percent off, according RetailMeNot’s data. Other peak times to buy are the end of September and during Cyber Week after Thanksgiving.

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