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 / Updated  / Source: TODAY
By Julia Curley

Grocery shopping is often filled with difficult decisions. Gruyere or Gouda? Gluten-free or grass-fed ground beef? Two bags of Goldfish or just one? These little decisions can add up in a big way by the time you get to the checkout counter.

But a new study shows that perhaps the most important food buying decision occurs before shoppers even enter the store. While many people might expect to pay a premium for organic produce or certain cuts of meat, according to the Dunnhumby retail preference index (which measures consumer data), food prices on the exact same items can vary widely by store.

Using publicly available financial data and information collected from 7,000 different household surveys, the Dunnhumby study ranked the top 13 “Winners in Price.” The following 13 stores were found to have the lowest prices on groceries overall:

  1. Aldi
  2. Market Basket
  3. WinCo
  4. Food4Less
  5. Costco
  6. Walmart
  7. Trader Joe’s
  8. Walmart Neighborhood Market
  9. Lidl
  10. Amazon
  11. H-E-B
  12. Peapod
  13. Sam’s Club

Aldi, a German grocer widely known for its great value, earned the top spot. In general, Aldi offers buyers a smaller selection of products when compared to giants like Costco — and features private-label options at lower-than-average cost, which is similar to Trader Joe's model.

Aldi, the crowned winner, currently has over 1,800 stores across 35 states. The chain plans to increase its retail presence to 2,500 stores by the end of 2022.Getty Images

Larger grocers, including Costco, Walmart and Trader Joe’s, followed Aldi on Dunnhumby’s list. But smaller regional grocers like Market Basket, a Northeastern chain; Winco, a West Coast and Midwest grocer; and Food4Less (which has stores in California, Illinois, Indiana, and Ohio) made the top five.

TODAY Food tested the data science analysis by comparing prices of a few items at six of the top national, brick and mortar grocers to see if the results measured up. It turns out that these stores differ in the items they stock, not just the prices at checkout. And, depending on the item, Aldi might not always offer the cheapest option.

Take a popular cereal brand, for example. Currently, Aldi sells a 15.4-ounce box of Honey Nut Cheerios in most of its stores. That single box costs $4.09 (27 cents per ounce). Meanwhile, Costco and Sam’s Club offer two 20.35-ounce boxes for different prices. At Costco, that Cheerios purchase costs $6.99 (17 cents per ounce), while at Sam’s Club, the same offering is $5.88 (14 cents per ounce).

And, of course, Trader Joe’s doesn’t even sell Cheerios. They offer “Trader O’s,” instead.

Buying in bulk at Costco or Sam'c Club can help you save at checkout.Getty Images

Dunnhumby ranked each grocer by its average checkout price, not just how individual items overall compared.

However, since every buyer’s grocery bill varies by the items they purchase, and Dunhumby's study did not take into account member rewards programs, it's important to check the weekly sales and deals on the products you're looking to buy.