If you’re a fan of United, or need more United miles (the more likely scenario), there is a great shopping app that you should know about:  MileagePlus X.

To put it simply, MileagePlus X is a shopping portal for United Airlines that is on your phone; however, it’s slightly different that other shopping portals in one major way:  you use your linked credit card to buy a gift card for the value of the things you’re buying.

First, download the app from the either the Apple App Store or Google Play. There is no harm in downloading, as it’s free!

Once it’s downloaded, you’ll need to log in with your United MileagePlus credentials and link a credit card. Then, you’ll see the list of nearby locations, or you can search for participating stores.

As you can see, you’re rewarded 2-5 times the number of points per dollar. Next, choose the store you wish to buy something from, and tap “pay now.” You’ll be brought to a screen that looks like the following:

Next, you’ll tap “pay now” again, and will be brought to a screen when you input the value of the items you’re buying.

As you can see, on Amazon, you’ll earn 2 United MileagePlus points for every dollar you spend (rounded down to the nearest dollar). Additionally, if you hold the United MileagePlus Explorer card from Chase, you’ll earn an additional 25% points, and the best part:  you don’t have to pay with your United card–just make sure it is registered in your account.

Once you input the value, you’ll press “pay now” a third time and your gift card code will come up. Make sure you have cellular service, or else it will time out! Once the code comes up, either input it yourself (if you’re shopping online) or hand your phone to the cashier. It may seem a little weird to do that, but I’ve done it a ton of times, and people generally know what to do. I always preface handing my phone over with “this is a gift card I have on my phone,” and I’ve never had an issue.

Finally, once the transaction has ended, make sure to tap “gift card redeemed.” It will then tell you how many United miles you’ve earned. These miles will be instantly deposited into your account.

So, now that you know how it works, here’s an example of how many United miles you could earn in a year, just by buying things you may already need. Over the course of this theoretical year, let’s assume you spend the following:

• $50 worth of Amazon goods a month (2 points per dollar)
• $150 at Gap twice a year (5 points per dollar)
• $150 at Banana Republic twice a year (5 points per dollar)
• $50 at PetCo four times a year (2 points per dollar)
• $25 at Barnes and Noble four times a year (4 points per dollar)
• $100 at Bed, Bath and Beyond twice a year (4 points per dollar)

In this scenario, you’ll earn the following miles per location:

• Amazon:  50 x 2 x 12 = 1,200
• Gap:  150 x 2 x 5 = 1,500
• Banana Republic:  150 x 2 x 5 = 1,500
• PetCo:  50 x 2 x 4 = 400
• Barnes and Noble:  25 x 4 x 4 = 400
• Bed, Bath and Beyond:  100 x 4 x 2 = 800

In sum, by buying things you already need, you’ve just earned 5,800 United miles. But wait, it can be better! If you have the United MileagePlus Explorer card, that 5,800 miles is actually 7,250 miles because of the 25% miles bonus. That’s nothing to sneeze at–last year I flew from Newark to Manchester, NH, the Wednesday before Thanksgiving for only 10,000 miles. With normal spend, you’re more than 70% of the way there!

Would you believe me if I told you it could get even better? Remember, whatever card you input as the mechanism for buying gift cards is ALSO earning points, as you also earn points for buying the gift cards to make these purchases. If you put all the theoretical purchases on your United MileagePlus card, that’s an additional 1,700 miles on top of the 7,250 you’ve already earned, making your earnings actually 8,950 miles!