Here are the states where egg prices have doubled — and the lucky few where they've risen by just 50%, according to new data

• Egg prices in some states doubled in December, compared with the same month in 2021, according to data from Instacart.
• States in the Midwest, including Iowa and South Dakota, were the hardest hit.
• Even so, the highest prices for a dozen eggs were in other states, such as Hawaii and Florida.

Egg prices rose so fast last month that in some states consumers were paying twice as much as they did just a year earlier, according to new data from Instacart.

States in the upper Midwest saw the average price for a dozen eggs double in December over the same month in 2021. The price rose the fastest in Iowa, where a dozen eggs jumped 153% to $4.44. 

Neighboring states also saw egg prices at least double. In South Dakota, they rose 137% to $5.00. Shoppers in Wisconsin paid an average of $4.78, an increase of 118%, according to Instacart. Consumers in Minnesota, Nebraska, North Dakota, and West Virginia also found themselves paying at least twice as much as they had the year before.

Iowa consistently produces the most eggs of any US state. In 2019, chickens on its farms produced just over 17 billion eggs, according to the U.S. Department of Agriculture. But the state's flocks, like those elsewhere in the US, have been devastated by avian flu, leading to higher egg prices and some shortages.

Despite the increases, states like Iowa still had some of the lowest egg prices in the US. Shoppers in Hawaii, where most food has to be imported from outside the state, paid $9.73 per dozen. That was the highest price anywhere in the country, even though prices rose just 51% in December, Instacart said. 

Florida was the second most expensive state for eggs, at $6.36 a dozen. Prices there rose 57% for the month. Instacart's data includes purchases that its customers made during the month.

Egg prices are likely to remain high in 2023. Cal-Maine Foods, the largest egg producer in the US, said in late December that it expects that the fallout from avian flu "will continue to exert downward pressure on the overall supply of eggs" well into this year. 

Farms that produce only organic or free-range eggs have been less affected by avian flu, leading to lower prices for those types of eggs than for traditional ones in some parts of the country.

The shortages are causing sticker shock among shoppers. Some are also facing empty shelves.

With demand so high, many supermarket chains like Kroger and Lidl are capping the number of cartons shoppers can buy. 

In December 2022, egg prices rose 11.1% compared to the month before, and nearly 60% more compared to December 2021, according to the latest Consumer Price Index stats. The index measures prices across all purchases, both online and at traditional retailers.

A search of Instacart in Orange County, California, on Thursday showed the price of a dozen cage-free grade AA eggs varying in price at supermarkets listed on the site from $5.86 at Walmart to $6.39 at Kroger-owned Ralphs. A 60-count carton at Costco cost $19.89.

Kroger CEO Rodney McMullen said he expects inflation to moderate later in the year, and projects egg supplies to normalize in the next few months as new hens lay eggs. 

"We're doing everything we can to minimize that impact," he told CNBC last week.