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Chipotle Guacamole is Free on July 31

There's no argument that Chipotle guacamole is really good; some people might even argue that it's the best thing on the Mexican food chain's menu. Normally, ordering guac with your Chipotle meal would set you back an extra charge of $2, which is why the chain's National Avocado Day deal is such a, well, deal.

To celebrate National Avocado Day on Tuesday, July 31, Chipotle customers can enjoy free guac with the purchase of an entree. There's one catch, though: You have to place your order online or through the Chipotle app. The special limited time deal doesn't work if you place your order in the store.

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"Our fresh, homemade guacamole has a massive fan following," said Chris Brandt, chief marketing officer at Chipotle. "We want to show our love for the avocado and reward our customers' guac obsession. Plus, it's a major bonus that you can skip the line when you order ahead with our app or at chipotle.com."

To redeem the free Chipotle guacamole offer, which is available only on July 31, customers can log in or create an account in the Chipotle mobile app or at chipotle.com. After selecting an entrée such as a burrito bowl or salad, customers can choose to add guac as an add-on, a side item, or as a regular order of tortilla chips and guac. To finalize the order before checkout, customers should enter the coupon code AVOCADO. The offer is not valid for in-store purchases and there is a limit of one free order of Chipotle guacamole per customer.

Chipotle uses 48 ripe Hass avocados in every batch of guacamole they make (which they make multiple times a day), plus lime juice, red onion, finely chopped jalapeño pepper, fresh cilantro leaves, and kosher salt. If you want to try your hand at making Chipotle's guacamole at home (in a medium bowl batch size), get their official Chipotle guacamole recipe here.

Watch: 10 Reasons for Taco Tuesday.