Attention Shoppers: You Underestimated Your Bill

A study in the Journal of Marketing shows that shoppers are not good at estimating the total cost of what they have in their shopping carts. Karen Hopkin reports

Illustration of a Bohr atom model spinning around the words Science Quickly with various science and medicine related icons around the text

Join Our Community of Science Lovers!


On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.


So, they’re scanning your items at the grocery store, and when the last tomato gets bagged you’re stunned at the cost. How did you spend so much? Maybe those cherries were 12 bucks a pound. Or maybe you should have paid more attention to what you put in the wagon. Then again, maybe not. Because a new study in the Journal of Marketing [see http://tinyurl.com/yl5dbxg] shows that the harder shoppers try to keep track of what they’re spending, the worse they actually do.

With the economy still in the dumps, sticking to a budget is key. And food’s a major expense. So a lot of shoppers try to keep a mental tally of what they toss into the cart as they go along. Scientists [Koert van Ittersum, Joost M. E. Pennings and Brian Wansink] interviewed 300 shoppers, and found that more than half of them try to crunch the numbers without a calculator or even a pen and paper. The trouble is doing that math in your head is hard. As a result, they underestimate their total cost, and end up overspending.

One trick, the scientists say, is to count what’s in your cart and multiply by a guesstimate of the average cost of the items. So nine things at $2 a pop should give you change of a twenty. It’s not perfect, but it’ll also tell you whether you can get in the 12 items or less lane.

—Karen Hopkin

[The above text is an exact transcript of this podcast.]

It’s Time to Stand Up for Science

If you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.

I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.

If you subscribe to Scientific American, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.

In return, you get essential news, captivating podcasts, brilliant infographics, can't-miss newsletters, must-watch videos, challenging games, and the science world's best writing and reporting. You can even gift someone a subscription.

There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.

Thank you,

David M. Ewalt, Editor in Chief, Scientific American

Subscribe