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A grocery shopping mistake that could be costing Americans money starts even before they get to the store, according to cookbook author Jenn Lueke.

"The No. 1 biggest mistake is just not taking the time to plan ahead," Lueke, Boston-based author of "Don't Think About Dinner," told Fox News Digital.

Making a grocery list and deciding what to cook for the week ahead can help shoppers save money and stress less about meals, she said.

SCIENTISTS SAY YOU'VE BEEN THROWING AWAY PERFECTLY GOOD MEAT BECAUSE OF ONE COMMON MISTAKE

Another source of overspending may be the pressure to make a different, impressive dinner every night of the week.

Planning meals before shopping can help save money and ease weeknight stress, Jenn Lueke says.…