The Grocery Trip Decides the Week, and It Isn’t the Impulse Buys
KEY TAKEAWAYS
- In one large Dutch study of supermarket shoppers, unplanned purchases were about a fifth of what people bought, not the 60 to 70 percent that gets repeated, and most trips had none at all. The problem on a hard Tuesday is usually the planned items that never add up to a meal.
- An online cart remembers last week for you. In a Cornell analysis of nearly two million trips, online baskets held less variety and more than twice as many repeat items as store baskets, which makes repeating easy and changing something you have to do on purpose.
- How often you should shop is a question about your week, not about virtue. A simulation of a four-person household found that predictable weeks suit fewer trips, and unpredictable ones suit more, smaller ones.
- Nothing here tests the one habit worth trying: plan the two worst evenings first and buy for those before anything else. That part is reasoning, and it is labeled as such.
It is 6:10 on a Tuesday. You open the fridge and the food is all there. Yogurt, eggs, a bag of greens going soft, a jar of something, half a loaf. You bought all of it on purpose on Sunday. And none of it, put together, is dinner.
That is the version of the story the usual advice skips. It says the trouble starts in the store, with the candy at the register, the endcap, the cart wandering off the list. If that were the whole problem, a list would fix it. Plenty of people carry a list and still stand in front of an open fridge at 6:10.
Here is the plainer claim. The grocery trip is a set of decisions made in advance for a tired version of you. It decides what is possible at 6:10, and it does that mostly before you leave the house.
Why the grocery trip is not an impulse-buy problem
The idea that most of what people buy is unplanned has been repeated for decades, with figures around 60 to 70 percent. David Bell, of the Wharton School, and colleagues Daniel Corsten and George Knox tested it against something better than exit surveys. They followed 2,945 shoppers at 21 Dutch supermarkets over two weeks in July 2006, covering about 18,000 purchases in 58 product categories. Unplanned buying came out closer to 20 percent, and over 60 percent of trips had no unplanned purchases at all. [1]
The same work found that who was shopping mattered more than the store. Shoppers who described themselves as fast and efficient made far fewer unplanned purchases than average, and larger and older households made fewer as well. [1]
Read that with its limits in view. The data are from the Netherlands, where many people walk or bike to the store, and they were collected in 2006. It says nothing about what any one person will do. But it moves the question. If most of the basket was planned, then a basket can be entirely planned and still leave you without a dinner. The failure is not the surprise item. It is the plan.
What the cart remembers
A lot of the shopping now happens on a screen. A team at Cornell, led by Sai Chand Chintala and Jura Liaukonyte, compared grocery orders placed through Instacart with in-store receipts for 4,388 households over three years, nearly two million trips in all. Online baskets had about 10 percent less variety, up to 7 percent fewer impulse items, and more than twice as many items repeated from one trip to the next. The study appeared in Marketing Science in 2023. [2]
What that means for you depends on what you are trying to change. The screen makes it easy to buy what you bought last time, and repeating it takes no effort. Making something different takes a decision, and the cart will not make it for you. The authors also point out they cannot say whether the shrinking variety is the shopper’s preference or the app’s design. [2] So this is a fact about how the tool behaves, not a verdict on online or in-store.
If your week keeps falling apart in the same place, look at whether the cart is just reloading last week.
How often, and why there is no right answer
A 2025 study by van Rooijen and colleagues modelled a four-person household planning meals over 21 days, shopping every one to four days, with three levels of surprise: a predictable household, one with occasional changes, and one with a dynamic week of unexpected guests and people eating elsewhere. Predictable households did fine with trips every few days. The dynamic ones did best shopping daily. [3]
It is a simulation, built around food waste, in a Dutch setting, with a fixed shelf life for ingredients and only simple disruptions. It did not model impulse buying, and no real family was in it. It does not say how often to shop. It says the right rhythm depends on how predictable your week is, which is a smaller and more useful claim. A week with fixed schedules can run on one big trip. A week that reshuffles itself is not failing at planning. It needs a different rhythm.
The step nobody tests
Here is the part I cannot support with a study, and I would rather say so than dress it up.
Before you write any list, look at the week and find the two evenings that will go badly. You usually know which ones. The late meeting. The child’s practice. The night everyone is home at different times. Buy for those two first. What you need for each is a meal you can put on the table in the state you will be in at 6:10, not the one you are in on Sunday. It does not have to be impressive. It has to be possible.
Only after that do you shop for the good evenings, the ones where you have time and energy and will cook anyway. Those evenings tend to be easier to cook for anyway.
If a household member does not eat the same way you do, or is not doing this with you, the same rule holds and gets harder. Ask what that evening actually looks like, and who is home.
Two smaller moves are worth trying and equally unstudied. Check what is already in the house before you write the list, so the trip fills gaps instead of repeating what is there. And write the list by evening, not by aisle: Wednesday’s things together, Thursday’s together. It costs a few extra minutes in the store. It saves you the moment in the kitchen when you realize the third ingredient is still on a shelf across town.
What this does not do
A better trip does not fix a bad week. Some weeks will go sideways whatever you bought, and the fridge will still be there on Thursday. Nothing in this article promises that any shopping method changes how you eat, and it does not need to. The claim is smaller: the trip decides what is possible on the hardest evening, and more of that decision is yours than the impulse-buy story suggests.
There is also nothing wrong with the fridge you have now. If the food is in the house, the plan is what is missing.
That is worth keeping in mind on the way home from the store. The trip that decides your Tuesday is the one you made on Sunday, and it is finished when the bags are put away. The next one starts when you sit down and look at the week.
REFERENCES
- Bell DR, Corsten D, Knox G. From point of purchase to path to purchase: how preshopping factors drive unplanned buying. Journal of Marketing, 2011;75(1):31–45. Summarized by Knowledge at Wharton, “Not on the List? The Truth about Impulse Purchases.” https://knowledge.wharton.upenn.edu/article/not-on-the-list-the-truth-about-impulse-purchases/
- Chintala SC, Liaukonyte J. Study of Instacart and in-store grocery purchases. Marketing Science, 2023. Read through the Cornell University news release; the paper’s exact title was not verified. https://www.eurekalert.org/news-releases/1006848
- van Rooijen MA, et al. Study of meal planning and shopping frequency under household uncertainty. 2025. Wageningen University repository; exact title not verified. https://edepot.wur.nl/694932
Diana Woods researches and writes about sleep, environment and everyday habit. She has no clinical training, and that shapes what this site does: instead of explaining what might be wrong with you, she reads the behavioural and environmental research and writes about the parts you can act on — the light in the hallway, the fifteen feet to the bathroom, what the morning does to the night that follows.
Every article here cites its sources, and she tries to include the parts researchers themselves flag as uncertain. Studies disagree, sample sizes are small, and correlation gets reported as cause more often than it should. Saying so is part of the job.
