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I have rarely, if ever, flown by the seat of my pants. I’m a planner by nature. I make lists, I weigh options, I do research. While this doesn’t exactly make me the life of the party, it does lead to significant savings when I shop, whether it’s finding a flight deal, like-new secondhand clothing, or major grocery savings.

Recently, I applied this mindset (skill? superpower?) to my first shopping trip at Costco, and it saved me a staggering 50% on my grocery total. Here’s how I did it, and how I’ll plan all my future shopping trips to Costco.

I also made sure to use a rewards credit card at checkout to earn cash back on my total. Check out these great credit cards if you’re looking for a card to shop at Costco.

Build a spreadsheet

Or, in my case, marry someone who is really good at building spreadsheets. When my husband and I started seriously considering becoming Costco members, we started writing down any items we thought of that might be good contenders to buy at the warehouse giant. Bulk dry goods like rolled oats, pantry staples like olive oil, and cleaning supplies like dish soap all went on the list.

Once we had a pretty thorough collection of items, we plugged them all into a spreadsheet and started looking up the prices we normally paid for each item, along with the sizes we usually buy them in. This gave us the per-unit price for each one.

Compare prices

Next, we went on Costco’s website to check what items from our list were available to buy in store. Some things got cut immediately — we eat a lot of rice, but as a two-person household, we don’t need a 25-lb bag of it. Others didn’t have comparable enough items at Costco — the brand of dog food our pup likes isn’t sold there.

For everything else, we entered Costco’s prices into the spreadsheet and did the same per-unit math that we did for the grocery store items. Bing, bang, boom, we had our answer as to which items were actually more affordable to buy at Costco.

A few examples: Coffee beans were $0.32 per ounce compared to the $0.70 per ounce we were paying. Dishwasher detergent pods were $0.12 per ounce rather than $0.39. And toothpaste was $1.23 per ounce instead of $2.03. But some items, including peanut butter and all-purpose flour, were actually more affordable at our regular grocery store.

One tip: Prices on Costco’s website may actually be a bit higher than the in-store prices, so your savings could be even more substantial on your final receipt.

Keep a running list

Now that we have this spreadsheet built up, we can add to it when we think of new items we want to buy (chocolate chips and face wash are running low around here!). And we can always refer back to it when we plan our next Costco trip, whether it’s in a few weeks or a few months, so we know we’re getting the lowest price possible for all of our groceries.

I know that doing homework is no fun, and it’d be more enjoyable to roam free in a Costco warehouse and go wherever the bulk-discount wind takes you. But if you can maximize your savings while shopping at Costco by doing a little research ahead of time, isn’t that worth it?

Top credit card to use at Costco (and everywhere else!)

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