If you're joining Costco, you get to choose between two membership tiers. Costco's basic Gold Star membership costs $65 per year, while the Executive membership costs double at $130.

At first, you might think that getting the more expensive membership doesn't make sense. But you should know that the Executive membership comes with one giant perk -- 2% cash back on your purchases. And if you choose the upgraded membership, you might come away $100 richer after a year.

How to score $100 in guaranteed Costco savings

You can save yourself $100 a year at Costco by searching for sales and stocking up on the items you use regularly at the right time. But there may be an even easier way to guarantee yourself $100 in Costco savings -- choose the right membership and rack up enough cash back to put $100 in your pocket.

As just mentioned, the Executive membership at Costco costs $65 more than a Gold Star membership. But thanks to the 2% cash back incentive, if you spend $8,250 per year at Costco, you earn $165. When you subtract the $65 cost of the Executive membership upgrade, you're ahead by $100. It's that simple.

Now, you may be thinking, "Yeah, but who spends $8,250 per year at Costco?" Well, believe it or not, it's not that hard.

Let's say you shop at Costco 24 times a year, or twice a month, and spend $250 per visit. That's not inconceivable if you're buying a lot of your family's groceries and household supplies from Costco. That alone comes to $6,000 per year in spending. And remember, that's just the run-of-the-mill purchases you need to function. The remaining $2,250 could easily come in several forms.

If you book a vacation package through Costco Travel, that alone could be well more than $2,250 if you're part of a big family taking a nice trip. And even if you don't have travel plans, you might need to replace a major appliance or some electronics at home. A new fridge, or a new laptop and TV, might get you to $2,250 in spending.

Also, some people stock up for the holidays at Costco by buying everything from decorations to gift wrap to presents for the numerous people on their lists. Depending on your approach to the holidays, you might end up spending somewhere in the ballpark of $2,250 right there.

Think about your Costco spending carefully

It doesn't make sense to overspend at Costco for the express purpose of racking up $100 in Executive membership cash back. But it does pay to think about how much you spend at Costco regularly, because even if you can't come away with $100 in guaranteed savings per year, opting for the Executive membership might still make sense.

Your break-even point for upgrading your membership is $3,250 in annual spending, because 2% of that sum is $65 -- the cost of the upgrade. So if you think you'll spend even $1 more than that, then it pays to choose the Executive membership, since you stand to gain something.

And if you're not sure what you spend at Costco each year and you can't simply review your credit card statements because you sometimes alternate with paying cash at checkout, here's an easy way to get that number. Just go to customer service and ask an employee to pull a record of your past 12 months of spending. If it's $3,250 or higher, then you'll know which membership is right for you.

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We're firm believers in the Golden Rule, which is why editorial opinions are ours alone and have not been previously reviewed, approved, or endorsed by included advertisers. The Ascent does not cover all offers on the market. Editorial content from The Ascent is separate from The Motley Fool editorial content and is created by a different analyst team.Maurie Backman has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Costco Wholesale. The Motley Fool has a disclosure policy.

Want $100 a Year in Costco Savings? Here's How to Get It was originally published by The Motley Fool