Buying in bulk is a hugely popular money-saving strategy in the U.S., where 83% of consumers use it, spending an average of $50 per week on such purchases, according to a new survey by TopCashback.

Unfortunately, 35% of them don't use up their bulk buys, and that waste takes a bite out of whatever savings they garner -- to the tune of $104 each year, on average.

"Bulk buying is always listed as one of the top ways to save money," said TopCashback Shopping Expert Chelsea Hudson in a press release. "Purchasing your items in bulk has many benefits for both you and your wallet but you have to be clever about it."

A man shops in a warehouse

Bulk buying can lead to waste. Image source: Getty Images.

What are people buying?

The most popular items on our bulk-buying shopping lists are the sorts of things that take a long time to go bad -- if they ever do. Toilet paper was No. 1, with 89% of bulk-buyers listing it as something they purchase that way. Notably, laundry detergent (60%) was the only non-bathroom item to make the top five.

Top 10 U.S. Bulk Buys

1. Toilet Paper (89%)

6. Freezer Bags (34%)

2. Laundry Detergent (60%)

7. Batteries (33%)

3. Soap (47%)

8. Bottled beverages (31%)

4. Toothpaste (43%)

9. Freezer Food (29%)

5. Shampoo and Conditioner (37%)

10. Meat (29%)

Data source: TopCashBack.com.

Why all the waste?

People often buy in bulk expecting to save money, only realize much later that they didn't, because their purchases expired, or that they simply didn't have any use for that quantity of the item in question.

It, of course, takes quite a while for toilet paper to degrade to the point of not being useful, but that's not true of most food items, and even things you don't think of as having an expiration date, like shampoo or cleaning products, can go bad.

One key factor behind the waste is that a full 50% of bulk buyers surveyed said that when they hit the warehouse store, they go in without a shopping list. Also, 30% said they buy items they aren't sure they'll need because they are on sale, while 4% make purchases they know they don't need.

The most common reason a bulk purchase goes partially or totally unused is that it expires (50%), but a close second is because it's simply forgotten about (48%). Overbuying not only wastes money, it causes 24% of bulk shoppers regret using the strategy, and 14% admitted they felt "financially worse off" for using it.

Have a plan

Bulk shopping can save you money -- but you need to have a plan, and a list. Know how much of each item you use, and match your purchase patterns to expiration dates. You should also consider issues like storage and practicality. A pallet of paper towels may be a great deal, but if they take over your house, you may feel less-than-happy about the purchase.

You should also consider your personal habits when buying in bulk. If you have two month's worth of candy in your house, the cost savings may not be worth it if easy access leads you to eat it in two weeks.

You should also consider splitting some deals with a friend so that both of your households can save money while keeping quantities reasonable. And as with all other types of shopping, don't get swept up by the idea of a sale -- if it's something you don't need, even a bargain price is too expensive.

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